PTERIDOPHYTES— LYCOPODIALES 



297 



strobili are treated for 24-48 hours with a 10 per cent solution of hydro- 

 fluoric acid in 70 per cent alcohol. 



The strobili of most species are square in transverse section. To get 

 longitudinal sections showing the relations of sporangia, sporophylls, 



Fig. 93. — Selaginella apus: longitudinal section of strobilus showing a microsporangium with 

 germinating microspores on the left; on the right, three of the four megaspores with gametophytes 

 near the archegonium initial stage; fixed in formalin alcohol, cut in paraffin, and stained in safranin 

 and light green; from a preparation by Dr. W. J. G. Land. X80. 



and axis, cut diagonally, from corner to corner, never parallel to the 

 flat side. 



Sometimes sections of the difficult later stages stay on the slide with 

 Mayer's albumen fixative. Even stages like that shown in Figure 93 

 should always stay on with Land's fixative. 



For archesporial cells, use iron-haematoxylin ; for young megaspores 

 and the development of spore coats, use safranin, gentian violet, 

 orange; for later stages use safranin and fight green. 



