Manchester Memoirs, Vol. li. (1907), No. 8. 5 



regards the vegetative organs, the explanation must, I 

 think, be a different one. For the Halonial stem described 

 by me (:03 s ) must have been a fully developed axis, as is 

 indicated both by its size and also by the secondary 

 thickening which it had undergone. The stem, too, of 

 which Fig. 1 of the Plate of this Memoir is taken was 

 certainly a mature stem, and yet the parichnos tissue is 

 entirely well preserved and obviously not secretory. The 

 better preservation seems to me to be entirely due to the 

 firmer nature of the mid-cortex, of which the parichnos is 

 an extension. On the other hand, quite young stems 

 of Lepidodendron selaginoides may have a defective 

 parichnos tissue, but then they have a defective middle 

 cortex as well. Of course if we assume the parichnos 

 canal to have been primarily a secretory canal, the more 

 defective might represent the more mature tissue. But 

 though admitting that the corresponding tissue in recent 

 plants is secretory, forming as it does a mucilage canal, 

 yet we may well suppose that in the more elaborate 

 Lepidodendracese the function may have been a different 

 one, though a secretory function is by no means excluded. 

 Hovelacque ('92), indeed, considered the parichnos strand 

 primarily glandular, and Renault, too, compared the tissue 

 to gum canals. If secretory one would expect the 

 tissue to end abruptly both in the leaf and in the stem as 

 it does in the recent plants in which it has been described 

 by Hill. But in the fossil plants the parichnos strand 

 goes off insensibly on the one hand into the mesophyll of 

 the leaf, and in the other direction into the mid-cortex of 

 the stem from which it is in no way separated off or 

 differentiated in structure, as can be seen in the best 

 preserved sections. 



Potonie ('97 and '99) has attributed to the parichnos 

 strands a transpiratory function, and compares them with 



