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PUBLISHED BY 
THE BIOLOGICAL CLUB OF THE OHIO STATE UNIVERSITY 
Vol. 1. JANUARY, J90I No. 3 
NOTES ON THE SELF-PRUNING OF TREES. 
John H. Schafpner and Fred J. Tyler. 
In a dense forest of growing trees the smaller, side branches of 
the main stem, as well as those of the larger branches, are continu- 
ally dying off. But the tree rids itself of these dead branches by 
forming a collar of tissue from the cambium layer around the base 
of the branch, which presses more tightly as layer after layer of living 
wood is added, until the branch finally falls off and the hole which 
is left is grown over in a short time. This process is known as 
natural pruning. But the process which we wish to consider is 
very different from this, and we desire to distinguish it by the term, 
self-pruning. In this case the living branches are cut off or else the 
cutting-off process is the cause of the death of the branch. A 
special adaptation is provided to accomplish the result and the pro- 
cess is one whose purpose is the shedding of the branches rather 
than the attempt to accommodate the plant to conditions of injury 
brought about by other causes. In a number of species perfectly 
formed winter buds were developed on the branches which were 
shed, and so far as our observations go, the twigs are cast in the 
fall and winter. 
Although the shedding of branches is well known, especially in 
the conifers, not as much notice has been taken of it as we think it 
deserves. We have been taking observations for several years and 
have been partly anticipated by I)r. Bessey in a note in Science 12. 
650, 1‘JOO, — Botanical Notes — The Annual Shedding of Cottonwood 
Twigs. Bessey describes the shedding of the twigs of Populus 
deltoides as occurring about the middle of October, and after giving 
the details of the process, concludes as follows: It is an interest- 
ing fact that the Tamarisks (Tamarix sp.) which are held by some 
botanists to be closely related to the Poplars, shed their twigs by 
exactly the same device as that described above. In the Tamarisks 
the shedding of the twigs is a part of the annual process of defolia- 
tion, their leaves being so small that it appears to be less trouble 
