Vol. 17 



TORREYA 



February, 1917. 



No. 2 



SELF-PRUNING IN THE AMERICAN ELM 



By Jean Broadhurst 



While self-pruning is not uncommon in trees, it is seldom as 

 noticeable as in the Carolina poplar; in early autumn branches 

 one to seven years old and ten to twenty inches long may be seen 

 lying under any young tree in such numbers as to give a most 

 untidy appearance to the street or lawn. 



Early in September, 1913, I noticed underneath some American 

 elms on the lawn just south of the Cornell library numerous smals 

 twigs, tw'o to four inches long, all as clean-cut at each end as if 

 cut by a sharp knife. On closer examination these ends were 

 found to be very similar to the scars found at the basal end of 

 self-pruned branches. While fingering some of the longer 

 tvvags, I was surprised to have them break in two in my hands. 

 These new breaks also occurred at the annual rings or scars 

 formed by the terminal bud scales. 



Fig. I shows a ten-year-old twig which was laid upon paper, 

 and pressed gently at each annual ring; breaks occurred as shown, 

 marking each year's growth. Fig. 2 shows a much more branched 

 twig with the same tendency to break at the annual bud scars. 

 The pruned branches of Carolina poplar are similarly cut off 

 at their bases; but careful examination of many twigs has failed 

 to show any tendency toward such breaks between the two ends 

 of any self-pruned branch. 



This raises a question with regard to the American elm; are 

 these successive breaks due to a definite but incomplete abscissal 

 •development or to a lack of satisfactory union of the growth of 

 any year with that of the preceding year. 



No. I, Vol. 17, of ToRREYA, Comprising pp. 1-20, was issued i February, 1917.] 



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