1920] CHILD &• BELLAMY— BRYOPHYLLUM 257 



shows that the low temperature is far more effective, even though 

 no visible injury results, than mechanical compression. 



These various experiments show very clearly that the domi- 

 nance of the chief growing tip of Bryophyllum may be overcome 

 to some extent at levels below the most apical five or six nodes 

 without separating the leaf from the plant or inhibiting the chief 

 tip, and in some cases by merely placing the leaf in water or in 

 moist air with its petiole gjid attachment intact. Such isolation, 

 however, usually results in development of only a part or a few, 

 often of only one or two of the buds on a leaf. Whether physio- 

 logical isolation of the leaf buds will occur as readily during the 

 summer months has not yet been determined. The fact that 

 injury to the petiole of one leaf may, if sufficient in degree, induce 

 growth of buds in the opposite leaf and often in the leaves of 

 adjoining nodes, shows further that the inhibition of growth of 

 buds in any leaf is due, not merely to the chief tip of the plant, 

 but to the opposite leaf and to some extent to other leaves also. 

 This fact has also been shown by earlier work and more recently 

 by Loeb's experiments. 



The results of cooling a zone of the petiole, however, are much 

 more striking. In these experiments a portion of the petiole 

 2-3 cm. in length is subjected to the low temperature, the rest 

 of the petiole and leaf being exposed to room temperature, and 

 the leaf blade more or less completely submerged in water, as 

 indicated in fig. 2, or by placing an open bowl of water in such 

 position that the leaf rests in the water. The succulent tissues 

 of Bryophyllum are very susceptible to injury by continued pres- 

 sure, and care must be taken that the low temperature coil does 

 not touch the petiole, that the packing of the coil is not too tight, 

 and that the petiole does not touch the edge of the jar or bowl in 

 which the leaf is submerged. In some experiments, particularly 

 the earlier, injury of the petiole resulted from one of these causes; 

 but although the results of the experiments on mechanical injury 

 indicate that the slight injuries thus produced had little or no 

 effect on the leaf buds, only those experiments in which no visible 

 mechanical injury of the petiole was found after removal of the 

 low temperature zone are regarded as entirely satisfactory. 



