I 7 2 
The Ohio A T aturalist. 
[Vol. II, No. 3 r 
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., Ouercus alba L. and Ulmus americana L. 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: Ouercus platauoids (Lam.) 
Sudw., Quercus Alexanderi Britt., Ouercus primus L., Rhamnus 
Fig. /. 
lanceolata Ph., and Ulmus racemosa Thom. The latter develops 
cleavage planes in the nodes caused by annual growth, the same 
as was described for Ulmus americana L. 
Two trees may be quite closely related and still act entirely 
different when it comes to the matter of self-pruning. For 
example, Ulmus americana L. has developed the self-pruning 
habit to a remarkable degree, while the process seems to be 
entirely absent in Ulmus fulva Mx. The same is true in the 
oaks. Quercus alba L- and Quercus acuminata (Mx.) Sarg. 
self-prune abundantly, while in our common 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 L., Q. palustris Du Roi., Q. coccinea Wang., 
