1892.] Phenomena and Development of Fecundation. 301 



changes of karyokenetic division but when the chromatin seg- 

 ments become visible there are only 12. The 12 segments are 

 found again in the division which succeeds in order to form 

 the pollen grain, Guignard assumes that during the forma- 

 tion of the mother cell the segments have united two and two 

 either end to end or parallel ; thus giving only 12. He thinks 

 it certain that this reduction in number can in no way be con- 

 nected with the elimination of nuclear, matter as seen in polar 

 globules. 



In the nucellus of the ovule the nuclei all possess alike 21 

 chromatin segments. The cell which differentiates to form the 

 embryo sac contains a nucleus which receives 21 chromatin 

 segments but when the nucleus of this divides, after a long state 

 of repose, they show a reduction, as in the pollen, from 24 to 

 12 segments and tiiese 12 segments are found in all the succeed- 

 ing divisions in the formation of the egg apparatus. A similar 

 phenomenal reduction is said by Hertwig to occur in the 

 animal kingdom, in the course of development of Amiris 

 megalocephala. 



Germination of Pollen and Growth of Pollen Tube .-—The act 

 ion proper consists in the union of the male nucleus 

 of the pollen grain with the female nucleus of the egg cell. 

 The mature pollen is transported from the anther where it 

 is formed, to the stigma by the aid of insects, wind, water, 

 etc. We are all. thanks to such men as Darwin and Lobbock, 

 more or. less familiar with the various processes by which pol- 

 lination is accomplished. The pollen brought in contact with 

 the stigma adheres there, being held and excited to germinate 

 by a sticky, sugary exudation which covers the stigmatic 

 surface. 



In germination the pollen grain sends out a tube which 

 grows down through the tissue of the style till it reaches the 

 micropyle or entrance to the ovule through which it passes, 

 enters the nucellus or body of the ovule, and comes in contact 

 with the embryo sac, at the upper point where the egg appar- 

 atus is situated (tigs. 30 and 37). It may well be asked how 

 the pollen tubes in their blind chase downward succeed in 

 finding such a small place as the micropyle and a single 



