£I7C (Dt^io Zlaturalist 



PUBLISHED BY 



THE BIOLOGICAL CLUB OF THE OHIO STATE UNIVERSITY 



Vol. I. JANUARY, J90I No. 3 

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NOTES ON THE SELF-PRUNING OF TREES. 

 John H. Schaffneb 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 Dr. Bessey in a note in Science 12. 

 650, 1900, — 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 



