CHAPTER XVII 



SOME PRELIMINARY EXPERIMENTS ON THE PATH OF 



THE ASCENDING AND DESCENDING SAP IN THE 



STEM OF BRYOPHYLLUM 



The experiments on polarity have led to the idea that the polar 

 character of regeneration in the stem of Bryoyhyllum is not due 

 to the chemical differences between the ascending and descend- 

 ing sap which in all probability exists, but to the fact that the 

 anlagen for shoots and roots are located in different tissues and 

 that under ordinary conditions, the ascending sap reaches primar- 

 ily the anlagen for shoots while the descending sap reaches 

 primarily the anlagen for roots. The inhibition of shoot forma- 

 tion by the descending sap is apparently a secondary phenomenon 

 caused perhaps by the fact that the descending sap reaches 

 primarily the tissues for root formation and for the growth of the 

 stem and that this growth in some way not yet cleared up inhibits 

 temporarily or permanently the growth of neighboring shoots. 



It was natural then to attempt to find out whether the ascend- 

 ing and descending sap flow in different channels. This might 

 be possible of demonstration, provided, first, that the channels 

 for the descending and ascending sap lie in different concentrical 

 layers in the stem, the one more peripheral than the other; and 

 second, that after removal of one type of channel no restitution 

 of the channels occurs by regeneration. 



In one set of experiments (Fig. 113) in pieces of stem split 

 longitudinally and consisting of two nodes and one leaf at the 

 base, the wood was removed in the upper part, between h and a. 

 Such stems still formed apical shoots, proving that the ascending 

 sap can reach the anlagen for shoot formation through the cortical 

 layers alone. In other experiments in pieces of split stem the 

 lower part of the wood between h and c (Fig. 114) was removed. 

 Such stems were still capable of forming roots at the base and also 

 shoots in the basal part. Hence the ascending and descending 

 sap can reach both the anlagen for shoots and roots through the 



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