42 LYCOPODIALES [CH. 



three fairly distinct regions; abutting on the endodermis is a 

 zone several layers broad of thick-walled cells constituting an 

 inner cortex modified for protection and support ; the central 

 region consists of larger and thinner-walled cells adapted for 

 water-storage and aeration; beyond this is an outer cortical 

 zone of firmer and thicker elements. The prominent leaf-bases 

 or leaf-cushions (fig. 125, A, Ic) give to the surface of a transverse 

 section a characteristic appearance which presents the closest 

 agreement with that of the younger shoots of Lepidodendron. 

 From the peripheral protoxylem groups small strands of xylem 

 are given off, which follow a steeply ascending course through 

 the cortex to the single-veined leaves. The leaf-traces, in several 

 species at least, are characterised by a mesarch structure 

 (fig. 125, F, G), the spiral protoxylem elements occupying an 

 approximately central position. The mesophyll of the leaves 

 varies in regard to the extent of differentiation into a palisade 

 and spongy parenchyma ; in all cases there is a single vascular 

 bundle occasionally accompanied by a secretory duct. 



In erect stems of Lycopodium, as represented by L. cernuum 

 (figs. 123,125, H, I), L. Dalhousianum, L. squarrosum (fig. 122) 

 and many others, the stele presents a characteristic appearance 

 due to the xylem plates being broken up into detached groups 

 or short uniseriate bands with the interspaces occupied by 

 phloem islands. This type of structure bears a superficial 

 resemblance to that in the single stele of certain species of the 

 fern Lygodiam^, but it is distinguished by the islands of phloem 

 scattered through the stele. In other species the xylem tends 

 to assume the form of a Maltese cross {e.g. L. serratum Thbg.) 

 or it may be disposed as V-shaped and sinuous bands termin- 

 ating in broad truncate ends composed of protoxylem elements. 

 This form of the xylem and the distribution of the phloem 

 groups are shown in fig. 125, D, E, drawn from a section of a 

 plant of Lycopodium saururus Lam. ^ collected by Mr A. W. Hill 

 at an altitude of 15,000 feet on the Andes of Peru. The 

 position of the protoxylem is shown fig. 125, E, px. 



1 Boodle (01) PI. XIX. 



2 This species is figured under the name Lycopodium crassum by Hooker 

 and Greville (31) PI. 224. See also Brongniart (37) PL i. fig. 1. 



