PINUS 191 



period of rest intervene? Compare it with Isoetes 

 or Selaginella in this respect. 



What changes would result in the formation of a 

 seed in Isoetes? What interferes with seed-forma- 

 tion in that group? What changes would interfere 

 with seed-formation in Pinusf 

 Define a seed. State several advantages to the 

 plant of the seed-habit. 



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 nee- 

 dles. 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. 

 Diagram the life cycle of Pinus as directed for 

 Isoetes (E, 3, p. 154), substituting pg( = pollen- 

 grain) for Jkf6 ! ( = male garnet ophyte), and es( = 

 embryo-sac) for FG( = female gametophyte). 



