278 



MORPHOLOGY OF GYMXOSPERMS 





m:' 



319 



320 



Figs. 319-321. — AraKcan'a Biduillii: fig. 



319, portion of the prothallial end of the pol- 

 len grain, showing two prothallial cells, each 

 of which has divided, giving rise to numerous 

 cells; the next division of the nucleus beyond 

 the prothallial complex will give rise to the 

 generative cell and tube nucleus; X666; fig. 



320, later stage, transverse section, showing 

 body cell in the center surrounded by nuclei 

 which have been set free bj' the breaking down 

 of the walls of the prothalhal cells; X666; 

 fig. 321, pollen tube with numerous nuclei; 

 on so small a scale the male nuclei and pro- 

 thallial nuclei could hardly be distinguished; 

 X54. — After LoPRiORE (104). 



after the pollen tube begins 

 to develop. Thomson (107) 

 has also observed many super- 

 numerary nuclei in the pollen 

 tubes of Araucaria, as manv 

 as thirty being counted. It 

 adds to the interest of this 

 situation when it is known 

 that the same condition exists 

 among the Podocarpineae 

 (Taxaceae), although the pro- 

 thallial tissue is not so ex- 

 tensive in that tribe. If the 

 two-celled prothallial tissue of 

 Abietineae indicates a more 

 primitive condition than no 

 prothallial tissue, as noted 

 above, is the many-celled pro- 

 thallial tissue of Araucarineae 

 (and of Podocarpineae) still 

 more primitive ? The only 

 escape from an affirmative 

 answer is to prove that the 

 tissue formed by the two 

 original vegetative cells is to 

 be explained physiologically 

 rather than phylogenetically; 

 in other words, that it is ceno- 

 genetic and not palingenetic 

 (p. 230). 



Another variation of general 

 importance is that observed 

 in the relative size of the two 

 male cells produced by the 

 body cell, and also in the com- 

 pleteness of their organization 

 as cells. Among Taxodineae 



