64 The Ottawa' Naturalist. [Aug. -Sept. 



shoot proceeds. Indeed, the much more restricted secondary 

 thickening of the vascular tissues to the boll strengthened my 

 belief. But experimental evidence is all against it. I removed 

 large sectors of tissue from the axis below leaves and below bolls, 

 in twenty cases" on August 19th. On the 2 1 st one boll was shed, 

 but the injury had been made beneath the corresponding leaf. 

 On the 22nd one, and on the 23rd two bolls were shed, the injury 

 having been made beneath them. After this there was no shed- 

 ding till the 28th, when two more bolls fell, beneath which the 

 operation had been done. In no case was the leaf affected, and 

 the shedding of bolls later than August 23rd must in any event 

 be excluded. The bolls were all small when shed, as the opera- 

 tions were done when the flowers were open. It can be shown 

 that the number of losses is accountable for in other ways, and 

 we must conclude that disturbance due to wounding is absent. 

 On the other hand. Balls (33), working in Egypt, was able 

 to cause practically complete shedding of leaves, flower-buds 

 and tolls within four days by pruning the roots, and so limiting 

 the ability of the plant to take up water. I have repeated the 

 experiment with positive, but less striking and perhaps not 

 unequivocal results, in North Carolina. Cultivation, which 

 unavoidably causes some damage to the shallower lateral roots, 

 is believed by planters to be responsible in part for shedding. 

 Such treatment as root-pruning is certain, if at all extensive, to 

 cause visible wilting in an unusual amount, and too great a loss 

 in this manner may interfere with the mechanism of abscission. 

 It would seem that, if a reduction of water activates the process 

 it must be when only in a small measure, such as we may suppose 

 happens in cut branches when kept in a moist chamber, a method 

 which was used even by von Mohl (34) in his studies. The 

 relation is, at the present moment, a ptizzling one. In the case 

 of flowers, Hannig was finable to find any effect on the rate of 

 abscission beyond that of ordinary laboratory air, buds, open 

 flowers and young fruits falling away equally rapidly in both. 

 Fitting arrived at the same conclusion, from which we may 

 argue that the greater loss of water by evaporation, supposedlv 

 attributable to drier air, has no effect on the abscission of the 

 corolla. This organ is, however, especially resistant, as is shown 

 by the fact that a cotton flower-bud, removed on the evening 

 before opening, will open and remain turgid on a laboratory 

 table for an entire day, even though the bracts and catyx wilt 

 and even wither. And I have observed that the petals of desert 

 plants (e.g., Sidalcea) remain turgid while the whole plant shows 

 marked wilting during the hottest period of the da}'. The fact 



i^Exp. 11, West Raleigh, N.C., Aug. 19th, 1913. 



