1909] CHAMBERLAIN— SPERMATOGENESIS IN DIOON 221 



THE POLLEN TUBE 



Whether in artificial cultures or in the nucellus of the ovule, the 



pollen tube begins to grow at once, emerging from the apex of the 



spore and growing out into the sugar solution or into the tissues of the 



nucellus. The tubes are irregular in diameter and sometimes have 



short branches, but they are nearly straight and lie so close to the 



surface that their position is indicated by brown lines radiating from 



the beak {figs. 19, 23). Since the haustorial portion of the tube 



reaches a length of 2 or 3 mm , the brown lines are easily visible to the 



naked eye. As the tube begins to form, the pollen grain end is pushed 



into the pollen chamber before the haustorial end has penetrated far 



mto the tissues of the nucellus. The tube is formed from the intine, 



*hich breaks through the exine and increases greatly in thickness, 



as may be seen by noting the comparative thickness of exine and intine 



m h s > 8 and 18. The difference is even greater than is indicated by 



the figures, because fig. 8 is more highly magnified than fig. 18. The 



tube stains a light brown with iron alum hematoxylin, contrasting 



sharply with the brilliant red which the exine takes when stained with 

 safranin. 



Starch is abundant in the pollen tube, and filaments looking like the 

 radiations about the blepharoplast, only much longer, are conspicuous, 

 specially in the vicinity of the nucleus. 



THE BODY CELL 



The division of the generative cell, giving rise to a stalk cell and a 



bodv 



le «ed later than the middle 

 completed . 



In characteristic cycad fashion, the prothallial cell now pushes up 

 ° the stalk cell (fi gs . IOj IIy I2j I$i j£). Stages between figs. 9 



co I0 ' which might show the cause of this peculiar and remarkably 

 °nstant behavior of the prothallial cell, were not available. 



until h b ° dy Cel1 ' Whidl is t0 P roduce two s P erms > does not divide 

 the'f foUowin g s P r ing. The division usuaUy takes place about 



week^ ° f Aprf1, bUt may ° CCUr a week earlier > or as late aS thC filSt 



fJl *? May ' During this P eriod of about half a year ' therC iS a 



31 S r °wth and differentiation of the body cell. 



