喜树形成层的发育及周年活动

喜树Camptotheca acuminata具非叠生形成层。形成层在进一步发育的过程中,纺锤状原始细胞的长度随着枝龄的增加而变长,射线原始细胞的长度随着枝龄的增加而变短。其形成层活动与大多数散孔材树种相似,具有明显的周期性。3月份芽萌动以后,形成层开始活动,4~5月份形成层活动最为旺盛,10月份以后进入休眠状态。淀粉储量的消长与形成层活动周期有很强的相关关系。3~4月份形成层恢复活动以后,淀粉储量逐渐减少甚至消失。8月份淀粉开始积累,9月份淀粉很快消失。11月份又重新积累,直到翌年3月份以后才开始消失。图1表1参12

Development and activity periodicity of cambium in Camptotheca acuminata

The cambium of Camptotheca acuminata is non-stratified.In the subsequent development of cambium,with the increasing stem age,the length of fusiform initials increases and the length of ray initials decreases.The cambial activity is similar to that in most trees of diffuse-porous wood and with an evident periodicity.In March,the cambial activity starts after bud sprouting,and it becomes the most vigorous in April and May.After October,it begins dormancy.Increasing and decreasing of stored starch are closely related to the periodicity of cambial activity.After cambial activity is resumed in March,starch decreases progressively until it disappears.In August,starch accumulates progressively and disappears quickly in September.The stored starch accumulates again in November until the next March,and starts to decrease after that.