1914] The Ottawa Naturalist. 73 



turgor changes the more important factor. They believe, 

 indeed, that in some instances chemical change is absent. 



The study of about 30 odd species leads me to the con- 

 clusio'n that chemical change is always present to some extent 

 whether growth and turgor changes intervene or not. I found 

 that under the influence of a hydrolysing agent (5% KOH) the 

 walls of the abscission cells break down more readily than those 

 of the neighbouring tissues above and below (Cheiranilms), and 

 may be so treated as to stimulate advanced autolysis, both in 

 the swollen condition of their walls and in their behaviour toward 

 stains. 



Concerning turgor effects it may be said that in such forms 

 as Ampelopsis and Impatiens, which present ideal material for 

 studv, the abscission cells show a no higher osmotic equivalent 

 at the time of abscission (of floral parts, peduncles, leaves) than 

 others. In the case of the axis, the cells of the cortex and 

 epidermis are pulled apart, apparently by elongation of the 

 central tissues, since in partially wilted peduncles the faces of 

 the abscission-wound remain juxtaposed, although abscission 

 actually takes place. 



Before, dviring or after abscission, secondary changes in 

 neighbouring tissues take place. They consist of suberization, 

 sclerification and lignification in various degrees, and all are 

 either extensions of periderm or are of the nature of wound 

 responses. This phase of the subject, beyond this ver}' general 

 statement, lies beyond the present purpose. Numerous details 

 have been worked out by Tison and by Lee. It is, however, 

 pertinent to indicate that, on the abscission of decurrent 

 peduncles in Gossypium there may follow an extensive sacrifice 

 of tissues, including all the living element of the stem, resulting 

 in the formation of a wound-cavity of sometimes large extent, 

 and not unlike gum pockets in appearance. Some of these 

 phenomena recall the abnormal behaviours seen by Loewi, 

 which, however, may readily occur in other species* (Ash, 

 Poplar, etc.) under special conditions. 



Citations. 



1. Correns, C. Vermehrung der Laubmoose. Jena. 1899. 



2. Tison, A. Recherches sur la chute des feuilles chez les 



Dicotyledones. Mem. soc. Linn. Normandie. 20:125. 

 1900. 



* At going to press, a paper by Gortner and Harris (Am. Jour. Bot. 1 : 

 48-50, Jan., 1914) on "An Axial Abscission of Impatiens Sultani as a result 

 of traumatic stimuli" comes to hand. They leave undecided the question 

 of the method of abscission. 



