42 ALTERNATING GENERATIONS 



These points are illustrated in the Gymnosperms, which the positive 

 evidence of the geological record shows to have been the primitive Seed- 

 Plants. Since the time of Hofmeister comparative morphology has arrived 



FIG. 28. 



. Pinus Laricio, showing a series from the formation of the tetrads to the development of 

 the pollen-tube. /, vegetative cells ; st, stalk cell ; b, body cell ; /, tube nucleus. X6oo. 

 (After Coulter and Chamberlain.) 



at the same conclusion, though along a distinct line of argument. Taking 

 examples from the Pinaceae, the sporophyte is represented by the Tree, 

 which is a large, much-branched, independent, and perennial organism, 

 with theoretically unlimited apical growth, and a highly differentiated 



