3 28 
The Ohio Naturalist. 
[Vol. Ill, No. 2 , 
seen shedding twigs by the thousands. Sometimes a twig would 
drop every few seconds. On May igtli the ground beneath this 
tree was covered with twigs and parts of tw'igs from one to six 
years old on an average of about ninety per square yard. When 
it is stated that the area thus covered was over ten yards in 
diameter some idea can be obtained as to the number of twigs 
pruned off in a few weeks. This tree was still self-pruning on 
June 3d. Many other trees were pruning at this time. The 
weather was very dry and it is the writer’s belief that dry weather 
accelerates the process of self-pruning. 
W. E. Britton* reports that when the fruit of the elm is ripe 
gray squirrels prune off considerable numbers of branches, and 
suggests that injury might be done to trees in this way. It 
would appear, however, that an elm tree which naturally prunes 
off hundreds of branches a year could not be injured materially 
by losing a few twigs which squirrels might bite off while feeding. 
The slippery elm (Ulmus fulva Mx.) does not self-prune 
branches, but it sheds large numbers of lateral buds every year, 
and has therefore no need of pruning off surplus branches. 
Foerstef has observed such a process in a number of trees. 
The cottonwood (Populus deltoides Marsh.) was found to self- 
prune occasionally from the time leaves appear in the spring until 
they are shed in the fall, although the main period of self-pruning 
is at the time of the shedding of the leaves. I11 a previous 
article, the black oak (Quercus velutina Lam.) was given in the 
list of oaks which are supposed not to self-prune. During the 
past summer, however, the writer found trees, on Cedar Point, 
Sandusky, Ohio, which were shedding a few small twigs by 
forming cleavage planes in basal joints. In late autumn the 
liackberry (Celtis occidentals Mx.) sheds considerable numbers 
of leafy twigs of the season by means of the formation of a 
brittle zone in the same manner as was described in a previous 
article for the fruiting twigs. 
The following plants, not mentioned in previous papers by the 
writer, self-prune by the formation of cleavage planes in basal 
joints : 
Juniperus virginiana L. 
Populus balsamifera I,. 
Populus tremuloides Mx. 
Coniptonia peregrina (L ) Coult. Mostly twigs of the season are 
pruned off. 
Quercus velutina Lam. 
Quercus imbricaria Mx. Self-prunes small twigs, but not abundantly. 
Euonymus europaeus L- Twigs from one to eight years old are self- 
pruned. 
* W. E- Britton. The Gray Squirrel as a Twig-pruner. Science 23: 950. 1902. 
f Aug. F. Foerste. The Identification of Trees in Winter. Bot. Gaz. iy: 180-189. >892. 
