GROUP III. PTERIDOPHYTA : LYCOPODIN^E. 



423 



stem and root have an axial vascular cylinder consisting of alternating bundles 

 of wood and of bast arranged radially : thus the stem is monostelic, and its struc- 

 ture only differs from that of the stouter roots in respect of the larger number 

 of bundles present : in smaller roots there is only one wood- and one bast-bundle. 

 In the stein the bundles frequently anastomose, more especially in the erect- 

 growing species, so that transverse sections taken at different levels present 

 diverse pictures. The wood-bundles consist of scalariform tracheids, with the 

 exception of the protoxylem. Neither stem nor root grows in thickness. In 

 both stem and root there is an endodermis, the cells of which have the charac- 

 teristic marking 

 when young but 

 eventually be- 

 come thick-wall- 

 ed and corky : the 

 endodermis does 

 not, however, ap- 

 pear to be the 

 innermost layer 

 of the cortex ; be- 

 tween it and the 

 vascular bundles 

 is what appears 

 to be a pericycle, 

 consisting of two 

 or three or more 

 layers of cells, 

 but this apparent 

 pericycle is really 

 the innermost re- 

 gion of the cor- 

 tex. The adven- 

 titious roots are 

 developed from 

 the pseudo-peri- 

 cycle of the stem. 

 The leaves of Ly- 

 copodium are of 

 very simple struc- 

 ture; they usual ly 

 have stomata on 

 both surfaces. 



In Phylloglossum, likewise, the growing-point of both stem and root has no 

 apical cell. The tuber consists wholly of pareuchymatous tissue. In each leaf 

 and root there is a single bundle : these bundles anastomose at the point of 

 origin of these members : when there is a sporangiferous shoot it contains an 

 axial strand of vascular tissue connected at the base with those of the roots and 

 leaves. The bundles are rudimentary and ill-de6ned. 



Erribryogeny of the Sporophyte. The early stages have only been observed in 



prock. 



emb. 



FIG. 276. Embryogeny of Lycopodium inundatum (x 42: after 

 Goebel): proth. prothallium; proth. tub. tuberous portion of the 

 prothallium; arch, archegonium; emb. tub. tuberous protocorm of 

 the embryo ; cot. cotyledon; st. second leaf, at the base of which is 

 the growing-point of the stem. 



