Manchester Memoirs, Vol. li. (1907), No. 8. 7 



atmosphere, enables the inner living tissues of the stem, 

 such as the cambium, for instance, to be supplied with 

 the necessary oxygen. The transpiration of the plant 

 is probably sufficiently maintained by the transfusion 

 tracheids which connect the vascular bundle with the 

 mesophyll of the leaf. A respiratory passage through 

 the dense outer cortex, and the impervious periderm 

 would seem to be an essential requirement of the Lepido- 

 dendroid stem. And as the vascular tissue of the leaf 

 trace cannot supply this want, a passage of parenchymatous 

 cells parallel to the leaf trace undertakes this function. 

 An examination of these parenchymatous cells in their 

 best preservation, shows that the tissue is well provided 

 with intercellular spaces. In some cases, indeed, the tissue 

 seems to have been more or less lacunar, and hence often 

 defective in preservation. If we were to look for a tissue 

 with analogous function among recent Lycopodiales, we 

 should probably find it in the trabecular tissue surround- 

 ing the stele of Selaginella. 



This view seems to me to be in complete consonance 

 with the actual structure of the parichnos strands seen in 

 their best preservation. It need not exclude the possi- 

 bility of the parichnos acting in a secretory capacity in 

 some instances as indeed Scott (:oo) has suggested. As 

 stated above the parichnos strands are visible when the 

 leaf has fallen av/ay, as two lateral marks on the leaf scar, 

 which is situated at the end or in the middle of the leaf 

 cushion in the different genera of the Lepidodendraceae. 

 The very distinct appearance of this strand on the leaf 

 scar is suggestive of its having still some part to play in 

 the life of the plant, and if its function was a respiratory 

 one, then the parichnos scars may be aptly compared in 

 function to the lenticels of the higher plants as indeed has 

 been done by Scott, Potonie, and others. This would 



