172 



The Ohio Naturalist. 



[Vol. II, No. 8, 



leaves were from time to time falling to the ground. Other plants 

 were observed shedding twigs with green leaves, among which 

 may be mentioned Populus grandidentata Mx., Salix nigra 

 Marsh., Quercus alba L. and Ulmus americana I,. These cases 

 seem to show that the formation of the cleavage plane is often 

 quite rapid, so that the leaves do not have time to wither before 

 the branches are detached. 



A considerable number of self-pruning plants were studied 

 which were not included in the former list. The following form 

 basal joints with cleavage planes: Quercus platanoids (Lam.) 

 Sudw. , Quercus Alexanderi Britt. , Quercus primus L. , Rhamnus 



Fig. J. 



lanceolata Ph., and Ulmus racemosa Thom. The latter develops 

 cleavage planes in the nodes caused b}' annual growth, the same 

 as was described for Ulmus americana ly. 



Two trees may be quite clo.sely related and still act entirely 

 different when it comes to the matter of self-pruning. For 

 example, Uhnus americana L. has developed the self-pruning 

 habit to a remarkable degree, while the process seems to be 

 entirely absent in Uhnus fulva Mx. The same is true in the 

 oaks. Quercus alba L,- and Quercus aciuninata (Mx.) Sarg. 

 self-prune abundantly, while in our connnou red oaks no such 

 process was discovered, although diligent search was made. The 

 following oaks failed to show any evidence of self-pruning : 

 Quercus rubra I^., Q. palustris Du Roi., Q. coccinea Wang., 



