14G MINNESOTA BOTANICAL STUDIES. 



figure,* the largest part being near the anterior end and the 

 posterior narrowed end being quite long (Figs. 17, 23, 24, etc.) 

 while his figures show the narrowed posterior Ccecum dilating 

 quite abruptly, making the posterior half of the mature sac quite 

 as large as the anterior half. Polygommi erectum the mature 

 sac is much more like Riimex than Polygommi divaricatum as 

 figured by Strasburger. 



Pecimdation, and the origin of the Sporophyte. During the 

 period of fecundation and the establishment of the sporophyte, 

 the embryo sac continues to increase in size rapidly, as may be 

 seen by comparing Figs. 24 and 33 and also 23 and 30, making 

 allowance for the greater reduction of Figs. 30 and 33. 



The first evidence of a pollen tube approaching or already 

 present in the sac is the disappearance of one of the syner- 

 gidae (Fig. 25). When actually present the tube is an easy 

 object to detect because it stains more deeply than surrounding 

 tissues, hence in those instances in which one synergid was 

 breaking down while no tube could be distinguished, I have 

 concluded that the tube was just approaching the sac. In Fig. 

 25 the tube has not yet discharged, as it shows two nuclei and 

 the end is intact, and it lies as usual beside the persistent syn- 

 ergid. The definitive nucleus here occupies a position at some 

 distance from the Qgg as it frequently does at this time. Here 

 this nucleus is in a resting condition, and I find it so constantly 

 up to this time. After the pollen tube has discharged the re- 

 maining synergid disappears, and the definitive nucleus soon 

 divides (Fig. 26). Though in some plants the definitive nu- 

 cleus seems to divide sometimes before the entrance of the pol- 

 len tube into the sac, its presence in the style probably furnish- 

 ing the necessary stimulus, it does not divide till after the 

 entrance of the tube in Riimex verticillatus and probably usually 

 not till after the fecundation of the egg. In the discharge of 

 the sperm nucleus the tip of the tube is ruptured as shown in 

 Figs. 26, 29, 30 and 35. After the pollen tube has discharged 

 a deeply stained spot may always be seen within the tube as 

 shown in the same figures. This is the shrunken second and 

 undischarged sperm nucleus. The fusion of the sexual nuclei 

 was only seen once, and in that instance the egg was badly 

 distorted. The tube in this case was closely applied to the egg 

 though the figures given herewith seem to indicate that this 



* Strasburger, E. 1. c. Fig. 21. 



