68 The Ottawa Naturalist. [Aug.-Sei t. 



of the laboratory was sufficient, according to Fitting, to produce 

 abnormally quick shedding of petals, this result following dosage 

 with carbon dioxide, tobacco smoke, chloroform, ether, and 

 other agents. Brown and Escombe (40) found that other organs 

 are similarly affected by disturbance of nutritive relations. 

 Hannig got similar results, except in the case of carbon dioxide. 

 0.00002 vol. per cent, of illuminating gas caused the abscission 

 of flowers (Mirahilis, etc.). A high concentration did not cause 

 this directly up to 14 hours exposure, but indirectly after 

 removal from the gas. Carbon dioxide, in concentrations up to 

 10 per cent., produced no effect, in accord with experiments of 

 Demoussy (1903, 1904, see Hannig). On the other hand, leaves 

 are shed if kept in air free of carbon dioxide (Loewi). It is 

 evident that more work on this point, as indeed on all others, 

 would be welcome. 



Light. Light is the source of energy for green plants, so 

 that much disturbance of this relation would be expected, 

 indirectly at least, to lead to abnormal behaviours. It would be 

 expected that changes in light intensity would have less effect 

 on floral parts than on green parts, but Hannig and Fitting came 

 to different results. Wiesner (39) believes that leaf abscission 

 occurs in early summer in the leaves less favourably exposed to 

 light because of the reduction of the absolute available light 

 ■supply. I miay observe that this kind of leaf-fall, as regards the 

 time of occurrence, takes places whether shade is present or 

 not. I have seen it on young plants of Negundo, which were com- 

 pletely illuminated, in which it seems more in accord with the 

 appearances to recall Dingler's paper, earlier cited. Leaves 

 shaded by the outermore foliage nevertheless do become yellow 

 and fall {Vitis, Ampelopsis, Euonymus, etc.), and the earliest 

 leaves in the White Birch in the autumn are those on the inner 

 branches, irrespective of their age. In the climate of Quebec 

 the question of high temperature is probably not important, 

 and in such cases it seems quite proper to explain this, in the 

 absence of more exact experimental observation, as due to the 

 reduction of light. 



The Time Required for the Act of Separation Proper. 



By this is meant the time occupied by the process of 

 separation itself to the exclusion of the period required to 

 institute it (latent period). It would seem on general grounds 

 that when cell division is involved, the process would require 

 more time than otherwise. In some organs (petals) in which 

 no cell-division occurs, the evidence (Fitting) shows that it may 

 be quite brief, less than 30 seconds indeed, but we cannot say 

 in any case exactly what it is. 



