30 



Ohio Naturalist. 



[Vol. 1, No. 3 



and expense to drop twig and all than to separate every individual 

 leaf. Possibly in the Cottonwoods, with their large leaves, we have 

 a survival of the Tamarisk twig-shedding habit long after its 

 original significance has disappeared." Dr. Bessey, however, we 

 believe, will not insist on this supposition when he considers that 

 the same thing occurs in species of Prunus, Quercus, and other 

 widely separated genera. 



Fig. 1 — Twig of Popukis alba, showing large basal joint and scars where smaller twigs 

 have been detached. 



Fig. 2 — View of basal joint of same twig as Fig. 1. 



Fig. 3 — Twig of Salix nigra, showing position of the brittle zone {a). 



Fig. 4 — Green twig of Ampelopsis cordata, showing joints («) at the leaf nodes. 



The self-pruning of twigs from woody stems, so far as our 

 observations go at present, is accomplished in three general ways: 

 1st, by the formation of a single joint close to the parent branch; 

 2nd, by the formation of a brittle zone near tiie base of the limbs 

 which are to be shed; 8rd, by a series of transverse joints corres- 

 ponding to the leaf nodes. 



