i 9 o8] BURLINGAME—PODOCARPUS 169 



time starch may or may not be present; later it becomes abundant 

 and occurs in relatively large grains (figs. 30, 31). The wall has a 

 thick exine much roughened on the outer surface and a distinct 

 intine. The spore coat is usually much thinner on the side away 

 from the point where the prothallial cells will later lie. The external 

 appearance of the pollen grain bears a considerable resemblance to 

 that of Pinus, except that it is smaller, rarely reaching more than 

 35 ft in the greatest diameter (exclusive of the wings). 



The microspore nucleus is large (fig. 18) and contains apparently 

 two sorts of material. There is a more deeply staining substance 

 distributed in irregular masses through a very fine ground substance. 

 As the nucleus prepares for division, the amount and density of the 

 more deeply staining substance increases in amount, assumes a more 

 definitely reticulated structure, and finally passes into a rather thick 

 and comparatively short spirem (fig. 2Q). This spirem breaks up 

 into the chromosomes (fig. 28), which often still show the distinct 

 segmentation into lighter and darker segments that has already been 

 referred to in discussing the sporogenous tissue. This segmentation 

 is not always found in the chromosomes or even in the spirem. It 

 might be supposed that the different appearance is due to differ- 

 ences in the depth of stain, but this does not seem to be true. 

 The chromosomes are rather long and considerably twisted at the 

 metaphase, but in dividing and passing to the poles they apparently 

 shorten up (fig. 31). What has been said of the first division applies 

 equally well to the next, so far as the few mitoses observed show. 



One or two prothallial cells are cut off and then the antheridial 

 initial divides to produce the tube nucleus and the primary spermato- 

 genous cell (fig. 32). In P. nivalis two primary prothallial cells, 

 which do not subsequently divide, seem to be the rule, though one 

 example of the division of the first prothallial was observed. The 

 pollen in the same sporangium varies in the stage of development 

 from microspores to the stage shown in fig. 32. These sporangia 

 were, in some cases at least, shedding their spores. 



In P. totarra Hallii one primary prothallial cell may be cut off, 

 after which the free nucleus divides to form the primary spermatogenous 

 cell and the tube nucleus (fig. 21) ; or two primary prothallial cells 

 may be cut off before the tube nucleus is separated from the primary 



