DEVELOPMENT OF THE POLLEN TUBE AND PROTHALLUS. 25 
cell, etc.). In his early studies the writer concluded from analogy 
with the development of the gymnosperms as described by Belajeff 
(2 and 3), Strasburger (109), and others, that a division of the second 
prothallial cell must take place. It, however, was only after pro- 
longed and diligent search that the evidence establishing this fact was 
finally secured, and only’a single tube has been found in all the many 
examined where the presence of a division was evident. This, how- 
ever, was fortunately in just the stage to settle the disputed point. It 
is in a telophase of the division when the two-daughter nuclei are 
reorganizing and the spindle connecting them is yet clearly evident 
(fig. 17). The first prothallial cell extending into the second pro- 
thallial cell is here clearly distinguishable, as in the preceding case 
described (fig. 15). The spindle, from the crescent shape of the sec- 
ond prothallial cell, assumes a position at an angle to the major axis of 
the prothallus, the lower nucleus and end of the spindle being crowded 
to one side by the position of the first prothallial cell, while the upper 
nucleus occupies a central position in the upper half of the cell which, 
when the new wall is formed, will become the central cell. The lower 
nucleus, which becomes the nucleus of the stalk cell, is already in this 
early stage noticeably smaller than the upper nucleus. Several round 
bodies which take a brilliant safranin stain in the Flemming triple 
process, and are evidently masses of nucleolar matter, are situated in 
the cytoplasm just outside of the spindle. The reorganizing daughter 
nuclei, in the only section secured in this stage, are too densely stained 
to show their structure well; they appear simply to be densely granu- 
lar. The spindle fibers show very plainly, but do not as yet show any 
thickenings in the center preparatory to the formation of a cell mem- 
brane. A most careful search has failed to reveal any suggestions of a 
centrosphere or centrosome at the apex of the spindle where one might 
be expected to occur. Ina number of instances a careful search has 
been made in the second prothallial cell, when it approaches division, 
for evidence of the presence of organs resembling blepharoplasts or 
centrosomes. Occasionally small centers with a few radiations have 
been observed (fig. 16), but these are irregular in their appearance and 
would seem to have no relation to blepharoplasts or centrosomes. 
The pollen tube at this time has reached a length of over 1 millimeter 
and starch grains have begun to appear, two being shown in the tube 
figured. Cells in the path of the tube are broken down and absorbed, 
apparently very little or no trace of them remaining. 
In Z. floridana in 1898 the division of the second prothallial cell 
was found to take place mainly between February 15 and March 5. 
In Z. pumila the same year the corresponding division occurred 
between February 25 and March 15. 
In a stage but slightly later than the above the central and stalk 
cells are found to be separated by a plainly visible plasma membrane 
thrown across the cell just above the apex of the first prothallial cell 
