128 



GYMNOSPERMS 



seen crawling over the sporangia and doubtless feeding on the pollen. 

 While the insects are so abundant in the male cones, they are rare in 

 the female cones, except that a beetle is common about species of 

 Encephalarlos. This beetle, however, bores into the female gameto- 

 phyte, destroying many of the seeds rather than furthering seed 



/3V 



/JS 



/36 



/37 



Figs. 134-137. — Dioon edule: fig. 134, microspore; fig. 135, germinating microspore; 

 P, prothallial cell; g, generative cell: fig. 136, exine ruptured by the young pollen 

 tube: fig. 137, later stage, with more starch: the generative cell has divided, forming 

 a stalk cell (5) and body cell (b). The prothallial cell (/>) is protruding into the stalk 

 cell; figs. 134-136, Xi26o; fig. 137, Xiooo. — After Chamberlain."^ 



production. Many of the insects observed are flying species, but 

 fertilization more than a hundred meters from a male plant is rare, 

 and, in collecting material, it is well to select female cones within 10 

 or 20 meters of a male plant. Nucelli from a female cone within 4 or 

 5 meters of a male cone may show 15 or 20 pollen tubes, while those 

 at 100 meters may show only 2 or 3, and female cones at a distance 

 of 200 meters may show only 2 or 3 good seeds or none at all. Any 



