Jan., 1902.] The Self-Pruning of Woody Plants. 
1 73 
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 in 
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 any 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 fragilis L. this process is also prominent, and small,, 
green branches were shed abundantly before August 13 th. 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, leaf}' 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 hackberry, 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. Occasionally some of the ordinary 
green branches are detached, the base becoming quite brittle. So 
far as observed, however, no special process of self-pruning: 
appears to be present except that of the fruiting branches. 
