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BOTANICAL GAZETTE 



presently examined in the light of the facts as they are now to be 

 presented. 



THE ABSCISSION ZONE 



While it is known that abscission in the internode occurs, in 

 general, near its base, it is impossible to connect it with visible 

 structural peculiarities, preformed specifkially with respect to the 

 process. Hannig says as much in admitting that, although fre- 

 quently or usually delimited by the smallness of the cells or the 

 occurrence of transverse divisions, these marks are not always 

 to be discovered. 



In very young internodes there is nothing at all to enable one 

 beforehand to fix upon the tier (usually one only) or tiers of cells 

 which become involved later. In older structures the configura- 

 tion of the cells for a short distance both above and below the node is 

 practically identical, and, although transverse walls are plentiful 

 in the prosenchyma, one cannot regard these as having any more 

 definite relation to abscission than the still older walls. Just as 

 abscission sets in one can frequently recognize the evidence of a 

 renewal of cellular activity in a zone of several tiers of cells, for 

 in these may occur many new, very thin transverse walls ("second- 

 ary meristem" of earlier authors). Abscission finally intervenes 

 usually at the upper limit of this zone (pi. fig. 4), and not in 

 the middle or below, although several tiers of cells may finally 

 take part. There is no other structural zone which deserves 

 designation in this connection. Since, however, even such a zone 

 as this occurs only sometimes in older organs, in which a general 

 rejuvenescence then appears to be demanded before abscission can 

 supervene, it can hardly enable us to delimit or define a reactive 

 zone. This zone of rejuvenescence is the "Folgermeristem" of 

 Von Mohl, in which his " Trennungsschicht " arises, and, as 

 Wiesner 6 has pointed out, the latter does not always arise in a 

 secondary meristem. Kubart 7 took the trouble to point out the 

 proper use of these terms, and there appears to be no good reason 

 to change their usage. 



6 Cber Frostlaubfall, etc. Ber. Deutsch. Bot. Gesells. 23:49. 1905. 

 'Die organischen Ablosung der Korollen, etc. Sitz. Akad. Wiss. Wien. 115: 

 1491- 1906. 



