340 



MORPHOLOGY OF GYMNOSPERMS 



certain species of Podocarpus (P. dacrydioides and P. jerruginea). 



In this feature, therefore, Microcachrys seems to be a transition form 



between Podocarpus and D ae- 

 ry dium on the one hand, and 

 Saxegothaea on the other. 



In the development of 

 the prothalhal tissue, two cells 

 are successively cut off, as 

 among the Abietineae, but 

 the peculiarity of the podo- 

 carps is that these cells usually 

 divide, resulting in extreme 

 cases in a tissue of eight cells. 

 A further peculiarity of this 

 tissue is that the walls break 

 down and the nuclei become 

 free, passing into the pollen 

 tube with the body cell and 

 stalk and tube nuclei (fig. 

 391). It must be understood 

 that these supernumerary cells 

 are not formed as are the two 

 original cells, that is, in the 

 series of divisions from micro- 

 spore to male cells, but rep- 

 resent a secondary and 

 variable product of the two 

 primary cells. The variability 

 may be indicated as follows. 

 In Phyllocladus (144) the 

 two prothalhal cells usually 

 do not divide, and the first 

 one begins to disorganize as 

 soon as it is formed (occa- 

 sionally persisting more or 



less), but the second one persists (fig. 392), and occasionally divides 



(174). This is exactly the behavior of the prothalhal tissue of 



Figs. 389-391. — Male gametophyte of 

 Dacrydium: s, stalk cell; 6, body cell; /, tube 

 nucleus; fig. 389, D. Bidicillii, Just after the 

 division into stalk and body cells; the two 

 prothalhal cells have not divided; fig. 390, 

 D. cupressinum, later s^age; both prothalhal 

 cells have divi^d;^'^g. 391, D. laxifoliiim, 

 showing the bodj^cell and tube nucleus, and 

 the nuclei of the stalk cell and of four pro- 

 thalhal cells; X960. — .\fter Miss Young (136). 



