566 



BOTANY 



PART II 



(b) Coniferae 



The development of the microspores of the Coniferae when they 

 germinate differs from the process described above. The prothallial 



- If 



FIG. 543. Development of the pollen-tube. A, B, Pinus laricio (x 300. After COULTER and 

 CHAMBERLAIN). C, Picea excelsa (x 250. After MIYAKE). p, Remains of the prothallial cells ; 

 up, spermatogenous cell ; m, antheridium mother cell ; s, its sterile sister cell ; g, generative 

 nuclei of unequal size in a common protoplasmic body ; A:, pollen-tube nucleus. 



cells, the number of which in the ancient genus Araucaria is larger 



than in the other Coniferae and the 

 Cycadeae, soon collapse (Fig. 543 

 A, B\ and the generative cells never 

 have the form of spermatozoids. 

 The gap between the Coniferae and 

 the Pteridophyta is thus a wider 

 one. 



The Abietineae have two genera- 

 tive nuclei of unequal size in the 

 one protoplasmic body ; only the 

 larger nucleus which goes first is 

 fertile (Fig. 543 (7, g). 



FIG. 544. Taxus baccata. Longitudinal section In Araucaria the prothallial tissue is 

 through the sporogenous tissue, showing an highly developed. The spermatogenous 

 embryo-sac mother cell which has under- cell gives rise to the sterile cell and the 

 gone the tetrad division ; three of the facul- antheridium mother cell. From the latter 

 tative macrospores are degenerating, while , , . , . , . , , . . , 



the fourth is undergoing further develop- ^vo generative nuclei, which to begin With 

 ment. (x 250. After STRASBUROER.) ar e ot equal size, are produced ; they are 



enclosed in a common protoplasmic mass. 



In many cases one of the two nuclei appears to gradually diminish in size. 



