PTERIDOPHYTES— LYCOPODIALES 



293 



10 n and stain in safranin and Delafield's haematoxylin. Safranin and 

 anilin blue or light green is good, and the light green gives particularly 

 clear views of the phloem. 



Lycopodium lucidulum is exceptionally good for a study of stem 

 structure, because one can pick out one-, two-, and three-year-old por- 



/ ^ '^\. 



%fMm 



Fig. 91. — Lijcopodium lucidulum: photomicrograph of transverse section of stem near the apex. 

 The five deeply staining groups of thick-walled cells are the protoxylem, and alternating with them 

 are groups of phloem cells; the large, thin-walled cells are metaxylem. Eastman Commercial Ortho 

 film, Wratten E filter (orange) ; arc light; Spencer 4-mm. objective. N.A. 0.65; ocular X6; exposure, 

 6.J seconds. Slide by Dr. J. J. Turner, negative by Dr. P. J. Sedgwick. X360. 



tions of the stem at a glance, by looking at the alternating groups of 

 sporophylls and vegetative leaves. During the first year, only the 

 protoxjdem, and not quite all of that, will be lignified. Early in the 

 second year, the lignification of the protoxylem is complete (Fig. 91). 



