1892.] Phenomena and Development of Fecundation. 



tub.-, lined by tliesc s| u i-in 1 i/.'-.l nourishing cells, lea. 

 the stigma down to the cavity containing the ovule: 



necessary for many tubes to penetrate the style, as it requires 

 one pollen tube to fertilize an ovule and there can be but little 

 doubt but that almost every ovule formed in the ovary, receives 

 a pollen tube and is fertilized. In the orchids one, by careful 

 dissection, can find a silvery bundle of the pollen tubes and 

 trace their progress from stigma to ovule. 



leads from the stigma down through the style, in the lower 

 portion of which it brandies into three parts, sending one 

 branch into each cavity of the ovary. The pollen tubes may, 

 with but little difficulty, be traced down through the stylar tube 

 to the ovary cavity and found in numerous cases entering the 

 micropyle of the ovules (figs. 3G and 37). 



In some cases the irritation produced by the growing pollen 

 tube through the tissue of the style, produces profound changes 

 even before it reaches the egg cell and empties its contents. It 

 has been observed, for instance in orchids, that at the time of 

 pollination the ovules are in a very rudimentary condition 

 and await the stimulus of the growing pollen tube, to develop 

 the egg apparatus and prepare for fertilization. A month 

 after the pollen tube starts its growth, the egg apparatus is com- 

 pleted and not until five weeks after this is fertilization com- 

 pleted. Similar phenomena have been observed in mul lein, etc. 

 It must not be thought that fecundation always requires so 

 much rime for its consummation, on the contrary it is usually 

 a very quick process, requiring only a few days at most in 

 flowering plants and much less in lower plants where the con- 

 tact is direct. 



Strasburger's Observations on the Immediate Process of Fecun- 

 dation.— On reaching the embryo sac, the pollen tube hardly 

 proceeds as we would expect. It does not penetrate into the 

 egg cell and then burst leaving a free passage for the genera- 

 tive nucleus. In most cases, at least, it does not even penetrate 

 the embrvo sac but the end of the tube spreads out over the 



