— 73 — 



few instances, and I have al'luded to these in a paper in press. At the time this 

 was in final revision, an additional brief article on "An axial abscission of Impa- 

 tiens Sultani as the result of traumatic stimuli", by R. A. Gortner and J. Arthur 

 Harris appeared (3). In it these authors report some inquiry into the effect of 

 injury on. and the method of, abscission of the stem in Impatiens Sultani, and con- 

 vey the impression that the phenomenon of axial abscission is a rare, or at any 

 rate practically unstudied, phenomenon. Though less rare than unstudied, it has 

 nevertheless received considerable attention. Instances have been studied by Cor- 

 rens (4) in the mosses by vonlloehnel (5), Vochting (6), Massart (7), Loewi (8) 

 and Hannig (9). 



The pertinence of a comparison of the phenomenon in the mosses and higher 

 plants I have indicated in my paper above cited. V^onHoehnel's work on abscis- 

 sion in twigs, though meagre, is sufficient to indicate that, so far as the living 

 tissues ar€ concerned, the process in twigs is not different from that in many 

 leaves, and this is borne out both by Loewi's work and by my own. Employing ex- 

 perimental means (injury), Loewi found that the amputation of the internode 

 (in Enonymns) is followed by abscission at its base, accompanied by a more or 

 less extended oedematous development in neighboring tissues. Vochting observed 

 the shedding of internodes after amputation in Hctcrocentrnm and Begonia, while 

 Massart saw the sam.e in Impatiens Sultani. Massart was, however, certainly wrong 

 in saying that injury is not followed by the formation of wound tissue except 

 below the abscission layer, and Hannig is also not in the right when he criticises 

 Massart, maintaining that the latter was probably wrong in not regarding the cell 

 division near the separation layer as belonging to the abscission tissues. From my 

 own observations I am satisfied that cell-divisions take no part in abscission in 

 this plant, and that those seen by Alassart are indeed an expression of wound 

 activity following separation. 



Hannig, working with peduncles and internodes, found that he could induce 

 their abscission by trans-section sufficient to cause material reduction of the 

 water supply, or by complete amputation, but that injury, no matter how exten- 

 sive, is not in itself efficient, and this I am able to confirm. Ampelopsis is to be 

 numbered among those plants which shed their internodes and tendrils both nor- 

 mally at the close of the growing season, and under experimental conditions, 

 while cotton (Gossypinm) bolls are readily caused to shed by certain kinds of in- 

 jury. Abscission of these parts may be induced by amputation, but severe injury 

 to the vascular supply bclozi' their insertions was found by me to be ineffective, 

 although their water supply must have been interfered with. 



Being primarily concerned with the method of abscission, I have re-exam- 

 ined Impatiens Sultani for comparison with some thirty-odd other species already 

 studied, since a delicate and succulent plant such as this offers especially good 

 material for the more critical examination of certain details bearing on this ques- 

 tion. Incrdentally, however, some facts have been gained which should be men- 

 tioned as bearing on the phase of the problem more especially considered by Mas- 

 sart and recently by Gortner and Harris. 



If an internode be cut off anywhere along its length, abscission will follow 

 either near to and above its base, or in a similar position in any internode below, 

 if leaves are absent. The farthest removed internode in which I have found it to 

 occur without the abscission of any of the intervening ones is the seventh. On 

 the other hand, it may take place in all the internodes at once, or successively. 



