CUEVATUEE OF BRYOPHYLLUM CALYCINUM. 341 



leaves of a plant growing in the ground, which had not grown any 

 roots or shoots in the notches of its leaves, were selected and they 

 were left dipping in water contained in a basin, on the 2nd of 

 December, 1919. Three days later on the 5th of December, roots 

 were found to have grown out from the submerged notches of the 

 leaf, to a length of nearly half an inch. On the 8th December, small 

 shoots also had grown out from the notches. 



These observations deny the inhibiting influence of root-pressure 

 and suggest the moist external conditions as accounting for the growth. 

 This is quite in consonance with the fact that the notches in the 

 leaves of the plants had grown out just after a week of heavy rain, 

 although root-pressure must then, presumably, have been considerable, 

 because of the very little transpiration that was possible. 



The following experiment appears to be conclusive. A pot plant 

 of Bryophyllam was taken and the stem of the plant was cut off leaving 

 only the last basal node with the two leaves attached. The cut end 

 of the stem was sealed firmly with Canada balsam, to prevent water 

 from being forced out and resulting in a diminution of root-pressure. 

 The axillary buds of both the leaves, were destroyed. One of the 

 two leaves was left dipping in a basin of water so that part of it was 

 submerged. On the 6th day, roots were found to have grown out in 

 clusters from the notches jDf the submerged portion of the leaf. Later 

 on small shoots also appeared. Here if, as seems probable, there was 

 considerable root-pressure, the formation of roots and shoots from the 

 leaf- notches was not in any way inhibited. 



Summary 



Experiments were made to determine whether special root-forming 

 and curvature-producing substances could be recognised as being 

 formed in the leaves, as assumed by Loeb on the results of his 

 observations on Bryophyllum calycinum. They were in the first 

 instance a repetition of his experiments, but with certain modifica- 

 tions to eliminate the effects of weight. We find no evidence in 

 support of the theory of special curvature-producing hormones, nor 

 of root-forming substances. On the other hand our observations con- 

 firm those of Klebs on the effect of an 'excess of water on adventi- 

 tious root-formation. 



A further series of experiments on the effect of the growth of an 

 axillary bud on the development of the marginal leaf-notches, failed 

 to confirm Loeb's results. All differences in the rate and amount of 

 growth of roots and shoots from the margins of the leaf, can in our 



2563—44 



