216 BOTANICAL GAZETTE [SEPTEMBER 
FERTILIZATION. 
The most interesting feature in connection with fertilization is the 
behavior of the pollen tubes. These begin to project through the 
openings in the exine about March 26, usually presenting a single 
tube for each pollen grain (fig. 15). While this is the general rule, 
it is by no means always the case, as many pollen grains were found 
developing from two to five tubes (figs. 18-19). In jig. 18 all the 
tubes seem to have had an equal stimulus to growth, but such is not the 
case in fig. 19. In this instance the largest tube was in contact with 
the stigmatic hair, which fact doubtless accounted for its greater size. 
Eventually one of these tubes gains the ascendency over the others 
which are drawn back into the microspore as it gradually shrivels and 
the tube elongates (jig. 17). This figure also shows the peculiar 
method of the young tube on coming in contact with the stigmatic 
hair, down which it almost invariably travels to reach the stigma. 
It was noted frequently that the tube when meeting the hair 
nearly at right angles would direct its course towards the distal end 
instead of towards the stigmatic end, as might be expected. After 
reaching the end of the hair the tube would often form a cyst-like 
enlargement before proceeding downward to the stigmatic tissue. 
The behavior of the pollen tubes within the tissue has been so 
accurately described by NAwAscHIN (16) for Ulmus moniana and 
Ulmus pedunculata that it will not be necessary to dwell upon 
their behavior in Ulmus americana. Suffice it to say, the same 
branching and apparently aimless wandering through the funiculus, 
integuments, and occasionally the nucellus which he describes was 
noted. In a few cases these tubes were found anastomosing about 
the micropylar end, as shown in fig. 22. The tube, after pre-sing its 
way through the micropyle, enters the nucellus near the tip of the 
beak (fig. 35) and passes directly to the upper end of the embryo Sa® 
The only cases where I observed branching were those of belated 
tubes entering the ovule after fertilization (figs. 21-22). Such tubes 
seem to have a general tendency to push toward the antipodal end of 
the sac. In fact there is some indication that they occasionally reach 
the chalaza. 3 
: The pollen tube is not easily disintegrated after fertilization, and 
is found intact, though staining feebly, until the embryo 45 
