THE SHRINKAGE OF RAYS AND FIBRES IN WOOD

1. Shrinkage was measured on sections of the woods of Artocarpusintegra, Canarium zeylanicum, and Acer pseudoplatanus.
2. Shrinkagestresses between rays and fibres were demonstratedby dryingradial strips of tissue containing rays on one sideand fibreson the other.
3. Strains developed by these stresses were removedby dissectionof the rays and fibres, which decreased the radialshrinkageof the rays and increased that of the fibres.
4. Thedifference between the radial and tangential shrinkage ofthefibres was reduced, but not removed by separation from therays,and this inherent anisotropic shrinkage of the fibresmust constitutean important cause of the differential shrinkageof wood.

     

VARIATION OF DENSITY IN THE WOOD OF PINUS PATULA GROWN IN KENYA

1. The specific gravity was determined for the individual ringsof twenty-three 13-year-old stems of Pinus patula grown in Kenyaand also separately on the early and late wood of six rings.
2. Significant correlations were found between specific gravityand both ring width and age ofthe ring from the pith. The effectof ring width was slight with more than six rings to the inch.
3. A comparison with Turnbull's data from South African treesofthe same species confirmed his results only in the firstninerings from the pith.
4. The mean specific gravity of theearly wood in five rings was0.368 compared with 0.469 forthelate wood. This high valuefor the early wood and the smalldifference between early andlate wood was due to the thicknessof the walls in the early-woodtracheids. Similar thickwalledearly-wood tracheids were observedin Kenya species of Juniperusand Podocarpus.

     

THE EFFECT OF RATE OF GROWTH (RING WIDTH) ON THE DENSITY OF SOFTWOODS

The relation between rate of growth and density has been examinedin fairly wide-ringed Douglas fir (Pseudotsugo taxifolia) andCorsican pine (Pinus nigra var. calabrica) grown in the southof England. A comparison between wood formed early in the lifeof the tree and wood of similar ring width formed later hasshown that the latter is invariably denser, indicating thatthe higher density of older wood is due to an age effect ratherthan to diminishing ring width. It is concluded that after acertain age rapid growth can produce wood of reasonably highdensity. This confirms that Turnbull's findings on widely spacedexotic softwoods grown in South Africa apply, with reservations,to trees grown in this country under conditions where rapidgrowth can be maintained.     

THE DISTRIBUTION OF MYCELIA IN EUROPEAN LARCH BARK, IN RELATION TO THE DEVELOPMENT OF CANKER

The paper presents fully evidence to support the following conclusions.

1. The living bark of European larch (Larix decidua Mill.) maybe expected to be infected with a microflora which containsboth fungi and bacteria and which may sometimes include Dasyscyphawillkommii (Hart.) Rehm.
2. The necrotic areas which constitutecankers can be found tocontain a similar flora including Cytosporaabietis Sacc., C.curreyi Sacc., and Coniotbyrium fuckelii Sacc.This flora mayinclude D. wilkommii but it is not necessarilythe most abundantnor is its presence necessary for the developmentof larch canker.
3. Inoculation experiments at Mynydd Ddu, wherecanker and die-backof branches is severe, with the above speciesof fungus, showthat inoculations stimulate extensions of deadbark. Under differentsite conditions and in a canker-free plantationat Southmoor,similar inoculations only produced extensionsgreater than thoseobserved in control treatments, where thetrees inoculated hadbeen partially girdled.
4. A mass of myceliumof the usual species inhabiting living larchbark may, undersuitable conditions, have an influence whichfavours cankerextension but some special stimulus, of whichthe conditionof the tree may be an important factor, is neededto enablethem to influence the living bark of the host adversely.Muchmore careful study is needed before conditions which accompanycanker development are accurately known.

     

CONIFEROUS LITTER AMENDMENTS AND THE GROWTH OF SITKA SPRUCE

The growth of semi-checked Sitka spruce (Picea sitcbensis Carr.)on heathland has been stimulated to different degrees by theannual application of litter of Scots pine (Pinus sylvestrisL.), Corsican pine (P. nigra var. calabrica Schneid), Lodgepolepine (P. contorta Dougl.), Japanese larch (Larix leptolepisGord.), and Sitka spruce, at rates corresponding to normal plantationconditions, following an initial heavier rate. Foliar analysissuggests that the response is at least partially attributableto the influence of the litters on the nitrogen nutrition ofthe spruce and differences between litters appear to be largelydetermined by their total nitrogen contents. In this respect,Japanese larch, with an annual needle fall generally greaterthan that of the pines and a higher nitrogen content, offersthe best promise as a nurse species for spruce.     

GROWTH STIMULATION OF FOREST TREE SEEDLINGS BY THE ACTIVITY OF FREE-LIVING MYCORRHIZAL MYCELIA

Observations by the late Dr. M. C. Rayner on a field experimentand the results of subsequent pot-culture experiments demonstratethat the soil activity of mycorrhizal fungi can improve thedevelopment of forest tree seedlings (Picea, Pinus, Betula)before actual mycorrhizal infection takes place. Further experimentsshow that ectotrophic mycelia are capable of stimulating endotrophictree species (Fraxinus excelsior, Cbam?cyparis lawsoniana, Robiniapseudacacia), i.e. that these ectotrophic mycorrhiza-formersbring about growth stimulation of the plant although no infectionis formed at a later stage. It is suggested provisionally thatat least some ectotrophic mycelia, Boletus scaber and Rbizopogonluteolus, may influence seedling growth by attacking soil organicmatter and liberating ‘nutrients’ from which thehigher plant benefits.     

Peridermium pini (Pers.) Lev. and the Resin-top Disease of Scots Pine: II. Lesion Anatomy

The stages in the formation of Peridermium pini lesions aredescribed. The hyphae of the parasite were septate, uninucleate,and intercellular, with unbranched haustoria penetrating allphloem cells and xylem parenchyma cells. Lesion extension occurredby apical growth of the hyphae along the outer edge of the functionalphloem. The hyphae stretched unbroken across the active cambium.Active centripetal and longitudinal growth of the mycelium occurredin the resin ducts of the xylem, the hyphae commonly reachingthe pith. Spermogonia were produced in late summer and fall,aecia appeared in spring. In lesion xylem, tracheids were shorter,rays taller, more numerous and wider, but ray cell height remainedunchanged. Fusiform rays increased in number and size and verticalresin ducts increased in number. Changes in xylem tissues didnot become evident until two to four years after invasion ofthe cambium by the mycelium. Invasion of the secondary phloemresulted in an increase in number and size of the longitudinalphloem parenchmya cells, while changes in phloem rays were similarto those in xylem rays.     

THE CHECKING OF FOREST TREES BY HEATHER

Experiments on podzolized heather moor at Allerston Forest haveshown that a heather mulch applied around checked Sitka spruce(Picea sitcbensis Carr.), Norway spruce (P. abies Karst.), andLawson cypress (Cbamaecyparis lawsoniana Parl.), or more simplythe elimination of living heather by surface hoeing, producesimproved colour and vigour of the trees. It has also been demonstratedthat the addition of a nitrogenous fertilizer to checked Sitkaspruce can, at least temporarily, alleviate the condition ofcheck.     

THE DISTRIBUTION OF MOISTURE IN THE LIVING STEM IN SITKA SPRUCE AND DOUGLAS FIR

1. Equilibrium in the moisture content of the stem appears to bereached at a given percentage of saturation rather than at apercentage based on the dry weight, and this method of expressingmoisture content eliminates many of the fluctuations apparentwith the latter.
2. Summer moisture content in Sitka spruce (Piceasitcbensis, Carr.)was highest on the site with the highestrainfall and lowestwith the lowest rainfall. It decreased inlate summer, suddenlyin Sitka spruce (in August) and graduallyin Douglas fir (Pseudotsugataxifolia Brit.).
3. There was asharp moisture gradient from cambium to heartwood,the saturatedzone being very narrow except on the wet Sitkaspruce site.In the Douglas fir it appeared that water couldbe withdrawnfrom the layers just behind the transpiration streamfasterthan it could be replaced, leaving this zone drier thanthesurrounding layers.
4. Lateral root pruning in Douglas fir ledto the drying out ofa narrow strip of tissue in the stem.

     

AN ENUMERATION OF THE MATURE OAK IN THE FOREST OF BERE

The paper describes the methods used in the field and in theoffice to determine the standing volumes and increments of 100-and 130-year old oak in the Forest of Bere, Hampshire, duringworking-plan revision. The figures obtained show that the standingvolumes and increments of sessile oak (Quercus petraea Liebe)are considerably higher than those of pedunculate oak {Q. roburL.) on the three sites investigated, namely, clays, sands, andgravels, while for both species sands appear to be the mostfavourable and gravels the least favourable soil types. Therewas little difference in the mean values for increment and standingvolume between the 100- and the 130-year old pedunculate oak.     

杨树溃疡病引致幼树的生长量损失估测*

杨树溃疡病经常在幼树干部形成大溃疡斑，造成枝枯和死树。以胸径下病斑面积与树周面积的比值计算的发病程度（X5）与胸径年生长量（Y2）之间呈显著相关。通过回归建立了三个品种不同病情下的生长量模型：美×559：Y2＝0．15406＋118．52194／（102．9113＋X^25)加杨：Y2＝－0．4136＋278．32113／（133．0115＋X^25)小×黑：Y2＝－0．08487＋110．16972／（131．4548＋X^25)三个估算模型经数学检验合理；坐标曲线符合植物病理学原理，可作为该病病情分级和生长量损失估算的参考。     

NATURAL REGENERATION OF PINE AND BIRCH ON THE HEATHER MOORS OF NORTH-EAST YORKSHIRE

Both pine (Pinus sylvestris L.).and birch (Betula pubescensEhrh.) usually invade after a fire, the invasion reaching greatestforce after 3 to 5 years, then falling off rapidly probablywith the return of the heather (Calluna). Pine seedlings onlygrow vigorously if their tap-roots reach the pan, when secondaryroots are developed extensively. In birch the tap-root is notwell developed, but secondary roots spread vigorously sendingdown sinkers to penetrate the pan. Regeneration of birch ishelped by rotten stumps and roots which its mycorrhizal rootsexplore. The root forms are compared and contrasted and thefindings compared with the work of Laitakari and Erteld.     

THE STORAGE OF ACORNS IN WATER

Acorns of sessile oak (Quercus petraea) will not tolerate prolongedsubmergence, but those of pedunculate oak (Quercus robur) survivevery well in regularly changed distilled water or tap-water.Survival is considerably worse in basic river water; the differencefrom tap-water is likely to be due either to the greater activityof organisms promoting decay, or to the prevalence of loweroxygen-tensions in river water. Storage in water under suitablycontrolled conditions might be a useful practical procedurewith pedunculate acorns.     

The Summerwood: Springwood Ratio in Conifers: How it arises, varies, and affects end use for timber, board, and paper

A theoretical discussion of variation in summerwood and springwoodcontents among conifers. Three methods of measuring these, bycross-sectional area of logs, by dryweight fibre percentage,and by nominal specific gravity, are compared. High-summerwood tissues have a nominal specific gravity of 0?45or over; low-summerwood tissues have a specific gravity below0?45. All conifers have a low summerwood content in their juvenilewood or core wood formed towards their stem-tips. In Pinus,Larix, and Pseudotsuga the summerwood percentage increases markedlywith age, but only in the outer layers towards the butt; inPicea, Abies, and Tsuga similar increases occur, but high-summerwoodtissues are seldom found. Within any species, and for any particulargrowth rate, low-summerwood tissues are characteristic of regionsof high relative humidity where summer water deficits rarelyoccur, such as high altitudes, far northern latitudes, and themaritime climate of western Britain. High-summerwood tissuesdevelop where summer temperatures are high, with associatedstrong sunshine, low relative humidity, and frequent summerwater deficits. High-summerwood tissues have greater strength in compressionand bending, relative to volume; but low-summerwood tissueshave greater strength relative to their weight. Low-summerwoodmaterial has proved satisfactory for most structural purposes,and for the manufacture of several kinds of artificial board.Its technical properties for the making of many types of paperare excellent, provided high resistance to tearing is not required.Likely summerwood content should guide planting programmes andmarketing policies.     

THE INFLUENCE OF HEATHER MULCHING ON THE GROWTH AND NUTRIENT STATUS OF LAWSON CYPRESS

The application of a heather mulch in a heathland plantationof Lawson cypress (Cbam?cyparis lawsoniana Parl.) has over aperiod of 8 years more than doubled the height of the treescompared with untreated controls. Analysis of the current foliageof trees from mulched and control plots reveals considerablyhigher concentrations of nitrogen and phosphorus in the former,indicating an increase in the availability of these nutrientsto the trees presumably from decomposition of the mulching materialand the suppression of the competing heather vegetation. Muchof the beneficial influence of the mulch must however be attributedprimarily to better moisture conditions, particularly duringdry periods when the superficial roots of the trees are otherwiseliable to desiccation.     

Studies on Ulmus: VII. Essex Elms

This biometrical study is based on a collection of nearly 500leaf samples from every ancient parish in the county. Most ofthe elms could be assigned to one of nineteen groups, 9 of U.carpinifolia, 1 of U. glabra, 2 of U. procera, 3 of putativeF₁ U. carpinifolia x U. glabra, 3 of U. carpinifolia with suspectedintrogression from U. glabra, and 1 of U. carpinifolia x U.procera. U. glabra is indigenous. Most of the U. carpinifolia appearto have spread out from six centres of origin, mostly near thecoast. These elms are very similar to forms now occurring innorth-west France, and it is thought probable that they wereintroduced from there, possibly by the settlers responsiblefor the Red Hills salt workings shortly before the Roman occupation.One group of U. carpinifolia came from Cambridgeshire via theEssex branch of the river Cam. Of the two main populations ofU. procera, that characteristic of south-east Essex is believedto have come from northern Kent, probably from the Hoo peninsula,while the group found in south-west Essex is probably a laterintroduction from further west. Hybridization between introduced U. carpinifolia and nativeU. glabra has occurred on a very large scale and putative F₁hybrids extend in a broad band across the county from the Hertfordshireborder to Suffolk. This hybridization most likely occurred duringthe clearing of the heavily forested part of northern Essexin pre-Conquest times. Subsequently, back crossing occurredbetween these hybrids and U. carpinifolia. Occasional hybridizationalso seems to have occurred between U. procera and the othertwo species. An outline of the probable history of the elm in eastern Englandas a whole concludes the paper.     

THE INFLUENCE OF WEATHER ON THE FREQUENCY OF BEECH MAST YEARS IN ENGLAND

Records are collected of beech masts (Fagus sylvatica L.) forthe period 1921–50 and these records are compared in atable with the temperature, rainfall, and sunshine figures ofthe 5 months, May to September, of the preceding summer. Itis shown that there are significant correlations between thesize of mast and (i) July air temperature and (ii) July sunshine.Other factors affecting mast are considered and in particularthe damaging effect of spring frosts to the flowers of beech.     

A Simple Method for the Routine Extraction and Quantification of Non-Structural Sugars in Tree Tissues

This paper describes a simple method for the quantificationof total non-structural carbohydrates in coniferous tissues.The method is based on a water extraction procedure and thequantification procedure utilizes p-hydroxybenzoic acid hydrazide,(p-HBAH). Results are compared with those from samples of knowncarbohydrate content and with an alternative established butlengthier procedure. There was good agreement in all comparativetests and the method is now routinely used for carbohydrateanalysis within the UK Forestry Commission.     

TWO-STORIED HIGH FOREST

The system has been adopted at Dartington with Japanese larch(Larix leptolepis), and it has been suggested that it worksthere because Japanese larch grows fast. It is argued in thispaper, however, that the system is best adapted to rather slowlygrowing trees, and the reason for its use with Japanese larchis that this species is characterized by a rapid height growthbut a small current annual increment, so that, unless the treesare isolated, they make extremely narrow annual rings. WithDouglas fir (Pseudotsuga taxifolia) and Sitka spruce (Piceasitcbensis) the annual rings might become too broad if thistreatment were applied, except at a rather advanced age. Nevertheless,the system has certain other advantages and, to attain these,it may be useful to adopt it more extensively, even if the annualrings become broader than we like.     

The Mode of Infection of Lodgepole Pine by Crumenula sororia Karst. and the Susceptibility of Different Provenances to Attack

Experimental inoculations of C. sororia on un-wounded Lodgepolepine produced successful infections after 9 months in 25 percent of cases, compared with 40–60 per cent where woundswere inoculated. After 16 months, however, these differencesdisappeared. The virulence of different isolates of C. sororiadiffered. Current year's shoots were more resistant to infectionthan 1-year-old shoots. Resistance was generally not a functionof broad geographical origin, save in the southern coastal types.Some provenances were highly significantly more susceptiblethan other closely adjacent ones: Burns Lake and Salmon Armwere highly susceptible, whereas Fort St. James and Mount Idaprovenances were respectively resistant. These observationsagree closely with field survey data, thus validating the useof young plants to indicate resistance of older crops to infection.