92 



MORPHOLOGY OP SPERMATOPHYTBS 



covered the true functions, the more prominent nucleus of 

 the tube cell was regarded as the generative nucleus. By 

 this time the large tube cell has become very full of starch, 

 and no further division occurs until 

 the following spring, a period of 

 about eleven months. In this con- 

 dition also pollination occurs, and 

 the old spore wall with its con- 



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SM)¥^ 



Fia. 70. — Pitius ian'eio, showing flattened 

 end of pollen tube before discharge into 

 the egg ; the two male cells are at the 

 tip and above them, but not shown, 

 are the nuclei of the stalk and tube 

 cells: X 500. — After C'iiameeklain. 



Fig. 71. — Pinus Zaricio, showing end of 

 pollen tube just before dischai'ge ; the 

 male cells (m, m) in this case are be- 

 hind the nuclei («) of the tube and 

 stalk cells ; s, starch grains ; the pit is 

 evident at the extreme tip ; x 500. — 

 After Coulter. 



tained gametophyte rests in the cuplike depression at the apex 

 of the nucellus during all this period. 



Dixon ^^ says that in Pinus silvestris the pollen tube is sent 

 out into the nucellus as soon as the grain is deposited, and that 

 it passes a year or even more in the upper region of the nucellus, 

 disorganizing the adjacent tissue and producing irregular cav- 

 ities. This seems to be true of Pinus Laricio also, whose pollen 

 tubes we have found in the nucellus in June. Coker reports 

 that in Taxodium distichum, however, the pollen tube, sent 

 out immediately after pollination, penetrates to the archegonia 

 without interruption. See Appendix. 



The pollen tube in Piwus begins to renew its penetration \ {' 

 of the nucellus during ^Vpril, about a year after the mother 

 cell entered upon the reduction division, the large tube nu- 

 cleus enters the tube, where it is completely invested by starch 

 grains, and at the same time the generative cell divides into 



