428 Scientific Proceedings, Royal Duhlin Society. 



Increased life duration. — Since petioles can be kept carrying large plants 

 for at least 15 months, it is possible that this increased duration of life 

 may in some way be bound up witli the increased development. Thus 

 Kuster (26), speaking of such a secondary development as we saw in the 

 tubers of Oxalis crassicanlis, denies that it is an activity hyperplasy. 

 " Durch die eigenartige Versuchsanstelluug," he says, " wurde die Lebens- 

 dauer der Kartofielknollen weit iiber das normale Zeitmass verlangert 

 die verschiedenen Gewebe der KnoUe wurden sehr viel langer als 

 unter normalen Verhaltnissen in Anspruch genommen. Nun ist offenbar 

 fortgesetzte Inanspruchnahme an sich noch niclit gleichbedeutend mit 

 gesteigerter Inanspruchnahme, es ware sehr wohl moglich dass auch 

 fortgesetzte Inanspruchnahme unter TJmstauden schon geniigt, um die 

 abnormale Bildung sekundarer Grewebe, wie sie Vochting beobachtete, 

 anzuregen." Similai'ly in regard to Mer's seven-year-old Hedera leaf he 

 speaks of " die infolge der abnorm verlaiigerten Lebensdauer fortgesetzte 

 Inaiispruchnahne." It is true that more recently (23) he leaves his position 

 with regard to Mer, referring his results now to the " Nahrstoffstauung die 

 bei Fortgang der Assimilation in den Blattern zustande kommt uud an die 

 vielleicht abnorm reichliehe Wasserversorgung die das neu gebildete Wurzel- 

 system der Blatter diesem zukommen lasst," but still he seems, in spite 

 of "Winkler's criticism, to retain his idea about Oxalis crmsicaulis. But his 

 argument of the effect of increased life duration has no force at all in tliese 

 experiments. If we refer to Plate XXXII, fig. 2, we see that the graft 

 was made on the 21st April, and cut down on the 2nd June — a bare 6 weeks. 

 Surely there is no question of increased life duration here to account for such 

 development — the petiole diameters increased from 3'6 by 2-8 to 47 by 

 4'0 mms. I think that without any further evidence this figure sliows that 

 the secondary developments occur before the question of the effect of 

 prolonging the life duration comes in at all, and that so this factor can 

 be ignored completely. 



Increased Storage of Nutritive Material. — If we recall Plate XXXIII, fig. 4, 

 the section of a leaf-cutting, we remember that a considerable quantity of 

 starch was to be seen in tlie petiole. The same phenomenon appeared in the 

 B group. It might now be suggested that this excess of carbohydrate was 

 responsible for the secondary thickening. Such is suggested by Mathuse (20) 

 to account for similar changes in his rooted leaves. That it is not the only 

 cause, or even a powerful factor, is shown by the fact that B and D petioles, 

 although, when removed, always so packed with starch that it seemed im- 

 possible for them to hold more in their cells, showed such very feeble secondary 

 development when compared with the A petioles. But that it may be a factor 

 in the B and U petioles is a consideration which cannot be ignored. This would 



