THE GYMNOSPERMS 261 



be obtained from greenhouses, and shows the macrospores and 

 microspores in good condition in winter and early spring. 



It is very desirable also to allow the students opportunity 

 to examine at least one typical Club-moss (Lycopodium) and 

 an Equisetum. 



Pedagogics. This is an important group from many points 

 of view. Ecologically it is important as the lowest large land 

 group, though its fertilization belongs to a water habit. The 

 alternation of generations, here at its plainest, should be 

 emphasized. The structure of the sporangia may be easily 

 made out fully. In Selaginella, the two kinds of spores 

 may be seen, but it is not possible to get the prothallus, 

 etc., and this must be described from pictures ; and if the 

 teacher is skilful, some idea can be given of the nature 

 of heterospory and of its significance in the transition from 

 Cryptogams to Phanerogams, though it must be confessed this 

 is a difficult topic for beginners. The relation of the Pterido- 

 phytes to the Hepaticse, through Anthoceros, should be empha- 

 sized, and the table of relationships given students as in Fig. 

 29. It is well to keep these trees of relationship constantly 

 before them, adding each group as it is studied. 



VI. The Gymnosperms 



92. What is the structure and ecology of the Pine ? 



Can you homologize the vegetative structure with 



that of the higher plants studied earlier by you ? 

 Can you homologize the reproductive structures 



with those of the Pteridophytes just studied? 



Or with the flowering plant formerly studied ? 



