Jan., 1902.] The Self-Pruning of Woody Plants. 173 



and Q. velutina Lam. It may be that the whole red oak group 

 is devoid of this habit. 



In some of our willows very numerous branches are developed 

 at the beginning of each growing season. It was found that iu 

 many cases a large part of these branches drop to the ground 

 long before the growing season is ended. A true basal joint is 

 formed and the twigs are cut off by the development of a 

 cleavage plane. This is therefore a process distinct from the 

 development of brittle zones in the ripe branches, which may be 

 one or more years of age. This process of shedding twigs of the 

 season is well developed in Salix interior Rowlee, our common 

 long-leaved willow. On July nth numerous branches of the 

 season were being cut off in this plant, some with leaves and 

 some with the leaves shed. The writer saw an}- number of 

 such branches on the ground under a patch of long-leaved 

 willows, and also many which would fall at the slightest touch. 

 In Salix fragiHs L,. this process is also prominent, and small,, 

 green branches were shed abundanth' before August 13th. The 

 same thing was observed in Salix amygdaloides Adrs. , although 

 it seemed to be much less developed than in the two previously 

 mentioned species. 



In some plants the branches of the season which bear the 

 inflorescence fall off after the fruit has matured, and in this way 

 the individual is kept in a properly pruned condition. This is 

 the case in Prunus cerasus L,., the common sour cherry, where 

 the short branches which bear the umbell-like clusters of flowers 

 drop off later in the season The same appears more prominently 

 in Prunus virginiana L. , in which the flowers are in racemes, 

 terminating short, leafy branches of the season. These drop off 

 after the fruit is ripe, and thus the shrub is kept well pruned, 

 since these short, flower-bearing branches are produced very 

 abundantly. 



Mr. Tyler called my attention to the hackberr}^, Celtis occi- 

 dentalis Mx., in which the slender annual fruiting branches also 

 drop to the ground during the fall and winter. These branches 

 dry off at the outer ends while the fruit ripens, and are then very 

 abundantly detached at the base, where a brittle layer appears to 

 be developed. It is interesting to note that the base containing 

 the brittle layer remains green for a short distance up the branch. 

 The writer has gathered large quantities of such branches under 

 fruiting hackberry trees. Many of the branches fall with berries 

 still attached, although usually the berries have all been shed 

 before the branches break off. Occasionalh' some of the ordinary 

 green branches are detached, the ba.se becoming quite brittle. So 

 far as observed, however, no special process of self-pruning 

 appears to be present except that of the fruiting branches. 



