PINUS 183 



8. Make a diagram (Xio) of the done as seen in longi- 

 tudinal section. 



9. Remove an entire stamen and observe that the 

 tip of it is turned up so as to fit over the end of the 

 stamen next above it. Suggest any advantage in 

 this arrangement. 



10. Make a drawing to illustrate this feature. 



11. Make a cross-section of the stamen and ascertain 

 of how many pollen-sacs it is composed. Draw. 

 The pollen-sacs of ths stamen constitute the anther. 



12. The structure of the stamina te cone shows it to be 

 in reality a simple flower. It is homologous to the 

 staminate flower of some of the higher plants. To 



! what in Zamia is it homologous? 

 G. The Young Male Gametophyte: 



1. Mount several mature pollen-grains in water and 

 examine with the high power.' 



2. Observe the body of the grain, and the two lateral 

 wing-like expansions, developed from the outer coat 

 of the pollen-grain. Suggest their use. 



3. Within the grain observe the tube-nucleus near the 

 center, and the generative cell near the wall farthest 

 from the wings. Look for the prothallial cell, 

 which frequently may be seen between the wall of 

 the grain and the generative cell. 



4. Make a drawing, 25 mm. broad, showing all features 

 observed under G, 1-3. 



5. The nuclear and cell-divisions which give rise to 

 these structures are steps in the germination of the 

 microspore. Into what does the microspore of the 

 heterosporus pteridophytes develop by germina- 

 tion? To what, then, in Isoetes or Selaginella, is 

 the mature pollen-grain of Pinus homologous? 



6. If prepared microscopic slides are available, more 



