176 MORPHOLOGY AND LIFE HISTORY 



tion in that group? What changes would interfere 

 with seed-formation in Pinus? 



6. Define a seed. State several advantages to the 

 plant of the seed-habit. 



7. To what, in the fern, is the endosperm of the pine 

 seed homologous? To what in the moss? To 

 what, in Isoetes or Selaginella, is the pollen-grain 

 homologous? To what in the fern? State, with 

 reasons, whether the leaves of the moss-plant are 

 homologous or analogous (or neither) to pine need- 

 les. In like manner, compare the organs of fixation 

 of the moss-plant, of the fern-plant, of the fern- 

 prothallus, and of the pine tree. 



8. Diagram the life cycle of Pinus as directed for 

 Isoetes (E, 3, p. 139), substituting pg( = pollen- 

 grain) for #w( = microspore), and es( = embryo-sac) 

 for W 



