STEM OF LYCOPODIUM. 



177 



in question recur with unimportant deviations. Our task will 

 be somewhat lightened by staining the cross-section with aqueous 

 solution of safranin, and the accompanying sketch (Fig. 70) will 

 give us some general information. In the cross-section of Ly co- 

 podium complana- 

 tum we find most 

 externally the epi- 

 dermis (ep) ; then 

 the cortex, the cells 

 of which at first 

 have wide cavities, 

 but farther towards 

 the interior dimin- 

 ish in width and 

 increase in thick- 

 ness, and so form 

 a firm sclerenchy- 

 matous sheath 

 (ve). The outer cells 

 of this sheath have 



stained more FIG. 70. Cross-section through the stem of Lyci 



i , -\ 7 '4.u ft. complanatu'in . ep, epidermis; re, outer cortical zone; vi, 



cnerry-n a Wltn tne inner cor ti ca l zone ; pp, innermost cortical zone ; sc, scal- 

 safranin ' the inner ariform tracheides ; ,s//, annular and spiral protoxylem ; v, 



bast (x 26). 

 strongly thickened 



cells more rose-red. The thickened elements of the cortex end 

 suddenly, and there succeed two or three layers of polygonal cells, 

 somewhat tangentially elongated, united uninterruptedly, and 

 staining cherry-red (vi). These cells are cuticularised, and resist 

 sulphuric acid well. Farther within follow several layers of 

 similarly wide-cavitied isodiametric cells, often containing starch, 

 with glistening, as it were swollen, walls (pp). With relatively 

 short action these have not been stained, but with longer are 

 orange-red. They form the innermost layer of the cortex. We 

 now notice the xylem strands, beautifully stained cherry-red. 

 They consist of broad scalariform tracheides (sc), in lateral 

 contact with one another, and, at the thin edges, of narrow 

 protoxylem elements. True vessels with perforated end walls 

 are not present in Lycopodium, though, for the purpose of com- 

 parison with other vascular plants, we may consider these xylem 

 strands to be vascular. The flat xylem bands in Lycopodium 

 complanatum run within the central cylinder, and more or less 



12 



