ANDERSON: EMBRYOGENY OF MARTYNIA LOUISIANA 149 
The two lobes of the sensitive stigma stand open just above 
the open anthers (FIG. 16), in the upper portion of the throat 
of the corolla, and the bee, entering the corolla tube, brushes 
the stigma, thus depositing the pollen that may be present on 
the upper part of its body and securing a new supply from the 
open anthers just below as it walks down the tube. The stigma 
is very sensitive when the flower first expands and the slightest 
touch will cause the lobes to close. If pollen be present 
they usually remain closed, but, in the absence of pollen, they re- 
open in from five to ten minutes. If pollen is witheld the stigma 
lobes may be made to close and open many times, but after one 
to three days the stigmas tend to lose their sensitiveness. 
However, this sensitiveness is not an index to the receptiveness 
of the stigmatic surface, for flowers hand pollinated after the 
stigma ceased to be sensitive and even after the corolla dropped, 
produced viable seeds. Viable seeds were also secured from 
flowers hand pollinated in the bud before the stigma lobes nor- 
mally opened. This was accomplished by gently forcing pollen 
between the closed lobes by means of a needle. In most flowers 
thus treated the stigma lobes never opened. At this time the 
anthers are still closed, but pollen from these as well as from 
open anthers was shown to be effective. 
FERTILIZATION 
Usually the pollen grains germinate immediately on the stig- 
matic surface, as was readily seen in material fixed one hour 
after the pollen was applied. At this time, many of the tubes 
were well into the tissue of the style. The growth of the pollen 
tube through the tissue, usually two or three cells from the 
stylar canal, is very rapid, for fertilization frequently occurs 
within six hours after pollination. The pollen tube is filled 
with plastids and granules that take such a dense stain that it 
is impossible to demonstrate the presence of the sperm nuclei, 
but, since the long, slender crescentic generative cell in the mature 
pollen grain shows only one nucleus, it is thought that the for- 
mation of the two sperms takes place in the tube. The pollen 
tube, as it grows nearly straight down through the style to the 
placenta, is comparatively broad and seems to retain its densely 
staining quality throughout the greater part of its length. 
