1892.] Phenomena and Development of Fecundation. 307 



nucleus after it has passed down the pollen tube divides, 

 and only one portion enters the oosphero digs. 41 ;nul -12), 

 the other remaining as waste nuclear matter and may ho 

 considered as a second polar globule. In the development 

 of the embryo sac it is thought the division of the nucleus 

 which gives rise to the nucleus of the egg cell and of the polar 

 nucleus which travels to the middle of the embryo sac to fuse 

 with a similar one from the basal tetrad, is one of the divisions 

 sought and that the polar nucleus lias in reality the signifi- 

 cance of a polar globule. If a second polar globule is formed 

 it is likely the preceding division, that which gives rise to the 

 first of the synergidse. If this is the case the regular after 

 division that forms the two synergidse may be looked upon as 

 corresponding with the rather abnormal but quite frequent 

 division which occurs in the first polar globule of many 



The instances cited of polar globules in the vegetable 

 kingdom, it will be seen, do not possess that definiteness that 

 is found in the animal kingdom. We fain would have greater 

 definiteness but further work is here necessary. Doubt clusters 

 about many questions connected with fertilization. We must 

 be content to take things as they are even if somewhat un- 

 satisfactory, until further investigation throws light on the 

 obscure points. 



Shaw School of Botany. 

 December 16, 1891. St. Louis, Mo. 



EXPLANATION OF PLATES. 



The figures are mostly redrawn or adapted from various 

 standard investigations. A few are original. 

 Plates XI-XIV. 



Fig. 1. A portion of the frond of Caulerpa, natural size. (Re- 

 drawn from Sachs.' Phys. of Plants, Eng. Ed. p. 492. 



Figs. 2-9. Iris pumila. Dividing mother cell of a stoma. 

 (Redrawn from Strasburger " Zellbild. und Zellteil. " (3rd. Ed. 

 1880.) PL yiii). Fig. 2. Resting nucleus. 3. Contraction and 

 breaking up of the nuclear thread. 4. Nuclear spindle. 5. 



