THE BASIS OF THE DIFFERENTIAL PHYTOTOXICITY OF 4-HYDROXY-3,5-DI-IODOBENZONITRlLE*

Summary. Entry of ioxynil-¹⁴C into portions of leaves was greater with mustard than with barley or pea and was unrelated to stomatal density. Measurement of ioxynil content of sprayed plants showed that by increasing the concentration of ioxynil and adding a surfactant, almost as much ioxynil could be made to enter barley as entered mustard from a lower concentration without surfactant. Auto radiographs showed that a limited amount of ¹⁴C was translocated to a small extent in plants following localized application of ioxynil-¹⁴C. An experiment comparing leaf removal by cutting with destruction of equivalent leaf areas by ioxynil treatment suggested a greater translocated effect of ioxynil with mustard than with pea or barley. Les principes de la phytotoxicité différentielle du 4-hydroxy-3,5-di-iodobetZonitrile II. Absorption et migration     

Parry's disease of pears is similar to pear decline and is associated with mycoplasma-like organisms transmitted by Cacopsylla pyricola

Mycoplasma-like organisms (MLOs) were detected by fluorescence microscopy in a number of pear cultivars and pear seedlings growing under a range of different conditions. In the cultivar Conference, MLOs were consistently associated with symptoms of Parry's disease, a decline-like disease of young trees with quince rootstocks. MLO-free pear seedlings rapidly became infected when they were planted outside. Experimental transmission of MLOs to pear seedlings and Conference trees was achieved using pear psyllids, caught outside or raised on infected plants under controlled conditions. Conference trees in an orchard trial remained free from the severe spring symptoms of Parry's disease when they were protected from feeding insects during spring of the previous year. MLOs were graft transmissible, but were not perpetuated by the standard propagation practices of budding or grafting when quince rootstocks were used. Parry's disease appears to be similar to pear decline, an MLO-induced disease well established in several other parts of the world. It is suggested that Parry's disease should be referred to as pear decline.     

THE DISTRIBUTION OF AVENA FATUA L., AVENA STRIGOSA SCHREB. AND AGROPYRON REPENS (L.) BEAUV. IN BARLEY CROPS IN THE WEST OF SCOTLAND

Summary. A survey of barley crops on 166 west of Scotland farms in 1969 indicated a more widespread distribution of Avena fatua L. than had previously been recognized. Whilst only 0·8% of the barley area was infested with A. fatua , the weed was found on 16% of the known barley-growing farms. A. fatua was associated with arable farming situations and with fields where there was a recent history of cereal cropping. Only on four of the sample farms where A. fatua was found had any attempt been made to control the weed. It is concluded that there is a strong case for eradicating or at least containing the weed before it becomes a major problem.
The distribution of Avena strigosa Schreb. and Agropyron repens (L.) Beauv. is also given.
Distribution d' Avena fatua L., d' Avena. strigosa Schreb. et d' Agropyron repens (L.) Beauv. dans les cultures d'orge de l'ouest de l'Ecosse     

The effects of rates of nitrogen application on seven perennial ryegrass varieties

The dry matter and crude protein production of the perennial ryegrass varieties S24, S23, Premo, Houba, Barlenna, Melle and Sceempter Pasture at annual nitrogen application rates of 212, 425, 637 and 1062 kg ha^?1 were studied for the years 1972–74 inclusive. The DM and CP response curves for the variety Melle were steeper than those for other varieties tested and levelled off at a higher N application rate. The results suggest that Melle is a variety with a genotype capahle of utilizing N more efficiently at higher rates than the other varieties tested.     

Further studies on Zschokkella russelli Tripathi (Myxozoa: Myxosporea) from Ciliata mustela L. (Teleostei; Gadidae), with emphasis on ultrastructural pathology and sporogenesis

Abstract In this second study of the myxozoan Zschokkella russelli Tripathi from Wales, infection occurred in 71-0% of five-bearded rocklings, Ciliata mustela L.; all infected fish were mature and immature fish were uninfected. Histologieal studies showed ehanges to gallbladder and liver that mostly conformed with earher findings, but sinusoidal dilation, which had not been seen previously, was present in three of 22 infected livers. Thickening around hepatic ducts was shown by transmission electron microscopy (TEM) to comprise fibroblasts and associated collagen bundles, while the attenuated epithelium of hepatic ducts bore few mierovilli. Zschokkella russelli plasmodia were seen by TEM to have fine tubular structures, particularly adjacent to developing sporonts. Spores showed long extensions to the sporoplasm, while spore valves had up to 18 surface ridges each and depressions between ridges were supported by microtubules. Otherwise, in its general ultrastructure and sporogenesis Z. russelli resembled other myxosporida.