328 The Ohio Naturalist. [Vol. Ill, No. 2, 



seen shedding twigs by the thousands. Sometimes a twig would 

 drop every few seconds. On Ma}- 19th the ground beneath this 

 tree was covered with twigs and parts of twigs 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 drN'and it is the writer's belief that dry weather 

 accelerates the process of self-pruning. 



W. E. Britton'-i^ reports that when the fruit of the elm is ripe 

 gray squirrels j^rune 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 naturall)' 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 occasional!}' 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. In a previous 

 article, the black oak ( Quercus velutina L,am. ) 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 

 hackberry ( Celtis occidentalis 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 jDrevious 

 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 balsatnifera L. 



Populus tremuloides Mx. 



Comptouia peregrina (L.) Coult. Mostly twigs of the seasou are 

 pruned off. 



Quercus velutina Lam. 



iQuercus imbricaria Mx. Self-prunes small twigs, biit not abundantly. 



Euonymus eurojxieus L. Twigs from one to eight years old are self- 

 pruned. 



* W. E. Britton. The Gray Squirrel as a Twig-pruner. Science ^5.- 950. 1902. 



t Aug. K. Foerste. The Identification of Trees in Winter. Bot. Gaz. /;.■ 180-1S9. 1892. 



