THE LYCOPODIALES 



261 



of stomata, ordinarily accommodated in furrows on the lower 

 surface of the leaf. The aeriferous structures of the blades of the 

 leaves were continuous with air-containing radial structures in the 

 outer and inner bark known as parichni. These are a noteworthy 

 feature of structure in the lepidodendrids and have attracted a 

 large amount of attention from students of the group. It should 

 be pointed out, however, 

 that they are by no means 

 a unique structure, since 

 special aerating devices 

 are likewise found present 

 in relation to the leaves 

 of the Coniferales. 



The roots of the lepido- 

 dendrids have been the 

 subject of much discus- 

 sion. Their ultimate 

 divisions, the so-called 

 stigmarian rootlets 

 (Fig. 187), are character- 

 ized by a very simple 

 organization, since only a 

 single group of protoxy- 

 lem is present. The root- 

 lets of this order divided 

 dichotomously, as is often 



FIG. 186. Leaf trace of a lepidodendrid 

 (after Scott). 



the case with those of the living Isoetes and Lyco podium. The 

 main roots of the lepidodendroid forms are in all probability only 

 partially known to us and present a curious type of structure. To 

 begin with, there is a large pithlike mass around which is developed 

 an extremely small amount of primary wood, at times so rudimen- 

 tary as to be scarcely recognizable. The small degree of develop- 

 ment of the primary structures and the quincuncial arrangement of 

 the lateral rootlets of Stigmaria have led to a great deal of doubt as 

 to their morphological nature. They have often been regarded as 

 creeping stems or rootstocks, and this view of their nature is found 

 even in recent literature on the subject. The mass of anatomical 



