THE OTTAWA NATURALI 



• 



VOL. XXVIII. JUNE-JULY, 1914 Nos.3ancl4. 



ABSCISSION.' 



By Francis E. Lloyd. 



Among' the ever recurring phenomena which characterize 

 the lives of plants, perhaps none is more impressive than the 

 usually sudden and complete loss of foliage by trees and shrubs 

 on the approach of winter, unless it be the untirnely occurrence 

 of the same change ensuing upon an untoward drought or some 

 equally unfavourable climatic disturbance. The uncouthness 

 and semblance of death attaching to a leafless tree when it 

 should be enfolded in a robe of verdure strikes a sad note, how- 

 ever little one may appreciate the exact nature of the importance 

 of leaves in the economy of the plant. And, when one enters 

 a tropical region, it is the everlasting verdure which at once 

 wakens the ijiterest. 



But the fall of the leaf is only one of a series of similar 

 behaviours, in many instances leading to an increase in in- 

 dividuals rather than a mere riddance of parts which are tmable 

 longer to resist the conditions imposed upon them. The multipli- 

 cation of simple plants, such as the algae, by a separation 

 between contingent cells, the breaking away of pieces of stem, 

 of leaves, brood-bodies and the like, so commonly occurring, 

 but usually unobserved, in the mosses (Correns, 1) ;the shedding 

 of leaves in plants which, like Bryophyllum and Begonia, use 

 them as a means to propagation by the growth of new plantlets 

 from the leaf -margins or elsewhere; the separation of staminate 



^The text of a lecture delivered under the little '"Abscission in 

 Flowers, Fruits and Leaves" before the Ottawa Field-Naturalists' Club, 

 Jan. 27, 1914. Although of a general nature, it includes the results of 

 original observations on a series of about 30 species, with especial 

 reference to the mechanism of abscission. The details of this phase of 

 the work are reserved for another paper, and a brief preliminary account 

 only is given here. All the work on the cotton, (Gossypium herbaceum) , 

 here reported was done at the Alabania Polytechnic Institute (account of 

 Adams Fund) or at West Raleigh, N.C., (accoimts of Bureau of Plant 

 Industry, U.S. Dept. of Agric. and of McGill University). 



