ro1t] HAGUE—DIOSPY ROS 37 
pletely enveloping the sac and extending around the stalklike 
nucellus and far up the micropyle (fig. 16). 
The study of the sac is made difficult by the dense outer integu- 
ment, through which killing fluids penetrate with difficulty, and 
also by the presence of chemicals which interfere with the stains. 
This last difficulty is especially true of the micropylar end of the 
sac, which when mature becomes a beaklike accumulation of a 
mucilaginous substance. 
Pollination and fertilization 
These studies have so far revealed only doubtful evidence of 
pollination and none at all of fertilization. Careful search has 
failed to show pollen tubes in the tissue of the style. The most 
positive evidence has been a few cases in which the mucilaginous 
substance has been divided in such a manner as to suggest a pollen 
tube penetrating the sac, and a few others in which there is the 
appearance of a swollen tip of a pollen tube within the sac. This 
evidence is discredited because the mucilaginous substance has 
been seen similarly divided too early for pollination, and the 
resemblance to the swollen tip of a pollen tube may be due to an 
incomplete or imperfect section of the stage shown in figs. 17a 
and 176. Other slight evidence may be found in the presence of 
the spindle and chromosome-like bodies of figs. 19 and 20b. These 
may possibly have entered the sac by way of the pollen tubes or 
may have originated from the nuclei of the tube. The fusing 
polars which are so conspicuous have been carefully examined 
for a third nucleus but none has been seen. 
The doubtful character of this evidence has naturally raised the 
question, whether pollination is essential to fruit and seed produc- 
tion. The field observations relating to pollination are limited and 
not very exact, but they suggest the possibility of an interesting 
problem. A tree in Decatur, from which material was collected in 
1906, bears seeded fruit abundantly, though no staminate tree 
is known to be nearer than two miles. In order to see if the pollen 
was carried that distance or was essential, a branch was covered 
in the spring of 1909 during flowering time so as to prevent the 
