Manchester Memoirs, Vol. li. (1907), No. 8. 19 



in structure between the leaves and root will undoubtedly 

 be used by those who believe in the morphological identity 

 of these organs in support of their contention. Never- 

 theless, we may, I think, equally well maintain, without 

 adopting that view, that in both cases for similar purposes 

 a communication has been established between the 

 aerenchyma of a lateral organ (leaf or rootlet) and that of 

 the axis (stem or rhizom) to which it belonged. It will, 

 I think, be obvious that the presence of an aerenchy- 

 matous strand running to the rootlets, lends additional 

 support to the view that the parichnos was concerned in 

 maintaining the respiration rather than the transpiration 

 •of the plant ; for the roots surely could have no trans- 

 piratory function to perform. 



The parichnos in the Lepidodendracese had the 

 function of taking in air through the leaf or through 

 the leaf-base, and of conducting it inwards to the stem and 

 downwards to the Stigmarian rhizom, and even into the 

 lateral organs (rootlets) of the same. The whole structure 

 of the parichnos and its mode of communicating with the 

 exterior is in consonance with this view. 



