K.— BOTANY. 203 



veloped by the transpiration of other regions draws these along down- 

 ward as well as upward channels in the wood. 



In thus ruling out the participation of the bast in the longitudinal 

 transport of organic substances in plants one naturally is forced to 

 speculate on its probable function. Its distribution and conformation 

 are such that, while it possesses a very small cross-section, it appears 

 with the other living elements of the vascular bundles, medullary rays, 

 wood-parenchyma, &c., to present a maximum surface to the tracheae. 



This large surface may find explanation in the necessity of inter- 

 change between the living cells and dead conduits. The colloidal con- 

 tents of the former render this process slow, hence the necessity for the 

 large surface of interchange to enable sufficient quantities of organic 

 substances to be abstracted from and introduced into the tracheae to 

 meet the needs of the plant. 



Before concluding I would like to add that the experimental work 

 carried out on this matter would have been quite impossible for me were 

 it not for the assistance and ingenuity of Mr. N. G. Ball. He has also 

 contributed materially by his criticisms and suggestions. 



