e 
BEHAVIOR OF THE POLLEN TUBE 97 
4 Diodia Virginiana 
In this species the conductive tissue is of a somewhat different 
character from that in the two plants already discussed. In the 
style both above and below the roof of the ovary the cells are 
cylindrical, their transverse walls being transverse, though oc- 
casionally oblique in varying degrees. The nuclei are not so much 
elongated, and correspondingly the length of the cells is not so 
great. The cell walls are thin throughout the whole range of 
stylar conductive tissue, excepting near the region of fusion of the 
basal and stylar parts of the partition where a slight thickening of 
the walls occurs. The conformation of the stylar conductive tis- 
sues is the same as in the other species. 
In the character of the conductive tissue of the ovule, how- 
ever, lies the greatest difference, a difference which, as we shall 
see, is connected with the behavior of the pollen tube. The tissue 
is disposed on the strophiole in a band around the insertion of the 
funicle, and extending downwards towards the micropylar region. 
The accompanying text figure 10 shows in a schematic way 
the arrangement. The component epithelial cells are approx- 
imately cubical in form (fig. 8), are fairly richly supplied with 
cytoplasm, and have a large nucleus. The outer walls are thick- 
ened, and exactly correspond in all respects to the homologous 
tissue in the other species studied in the young condition, before 
any further changes take place, 2. e., before the cell elongates into 
columnar form. At the time of pollination, a mucilaginous secre- 
tion appears so that at this time there lies on the surface of the 
conductive tissue a layer of mucilage of a thickness of nearly half 
the depth of the cells. The mucilage may be traced between the 
cells to some depth. 
This conductive tissue corresponds in general to that which 
has been described by Dalmer (3) as occurring on the placenta in 
certain Liliaceae both in form and in the occurrence of the muci- 
laginous secretion through which that author has shown that the 
pollen tubes grow, and from which they derive nutrition which 
enables them to grow onward toward the micropyle. Apparently 
similar cells have been described by Lang (5) in Byblis and Poly- 
pompholyx. 
