CLUB-MOSSES AND THEIR ALLIES. 143 



rangium opens. From their small size, as com- 

 pared with those produced in the macrosporangia, 

 these are called microspores. With the high power, 

 observe 

 a. The form of the microspores. Are they strictly 



spherical? 

 h. Their structure, particularly the spiny exospore 

 and granular contents. 



IV. Remove a macrosporangium from the lower part of 

 a fertile branch and examine on the slide, using first a 

 good lens, and afterwards the compound microscope. Ob- 

 serve 



1. The obvious external differences by which this is 



distinguished from the microsporangium. 



2. The number of spores contained in the sporangium. 



From their relatively large size, these are called 

 macrospores. 



3. The structure of the macrospores. This is readily 



made out by simply treating with potash solution, 

 and dissecting away the hard external coat. After 

 removal of the exospore, the smooth, light-colored 

 endospore is found, and the contents of the spore, 

 chiefly oil and aleurone grains, with the mass of 

 cells composing the pfothallium, are plainly seen. 

 Sectioning must be resorted to, if these are shown 

 accurately in position ; but all of them can be 

 recognized easily and satisfactorily by following 

 the treatment suggested. 



Note. — It is important that these parts should be clearly seen 

 and mnderstood. In Selaginella the prothallium is formed before 

 the spore has left the mother plant, and it is still for some time 

 enclosed in the macrospore, which also contains a large amount of 



