THE OTTAWA NATURALIST 



VOL. XXVIII. AUGUST-SEPTEMBER, 1914 Nos. 5 and 6. 



ABSCISSION. 



By Francis E. Lloyd. 



(Continued from page 52) 



This dependence upon external conditions is frequently 

 illustrated by the behaviour of plants in temperate and boreal 

 regions. The weather conditions about Montreal during October 

 and November of the 5-ear just past (1913) were peculiar, and 

 they were reflected in the behaviour of shrubs and trees. Many 

 of them began to push out their spring flower buds, and in some 

 instances {Hydrangea) partially opened their flowers, while the 

 usuallv prompt disappearance of foliage in many trees and 

 shrubs was much delayed. The poplars were especially notice- 

 able, retaining their leaves even in exposed situations so that 

 manv were retained far into November, while a few still remain 

 at the present writing. Ampelopsis Veitchii was also note- 

 worthv in this respect, the conditions having been such that, 

 in some cases, a full half or more of the leaf complement still 

 remains adherent, though dry and dead (February, 19H). 

 I examined these plants and found that the process of abscission 

 had been started, but had been prevented from completion. " 

 Perhaps, having been delayed by the unusual prolongation of 

 warm weather, the abscission was overtaken by a sudden change 

 and stopped by killing the leaves, whereas, normally, the 

 abscission would have been completed before such intervention. 

 It is possible that an examination of such trees as the black-jack 

 oak, which often fails to shed its leaves, would throw light on 

 this habit. A red beech, planted on the campus of McGill 

 University, constantly retains its leaves, but those especially 

 on the shorter lateral shoots. According to my late colleague, 

 Professor Alcock, this tree shows each year an increasing 



^ Tison found that the marcescent leaves of Hamamelis differed 

 from the normally caducous in having an incomplete abscission mechanism 

 or it is not even initiated. 



