140 A. H. Graves, 
to go into a lengthy description. For the sake of completeness, 
however, I will review the more important points, noting a few minor 
differences from Murbeck’s results, and adding a few observations 
of my own. 
We may regard the history of the male gametophyte as beginning 
with the appearance of the synapsis stage in the pollen mother-cells, 
which precedes the first reduction division and signalizes the special 
preparations for that process. Seven different flowers chanced to be 
fixed during this stage, and the appearance of the pollen mother- 
cells in all was typical (PI. XI, fig. 87). The nuclei are very large, 
but no knoblike processes are appended to them, such as Wiegand 
(1899) figures for Potamogeton foliosus. Although some such appear- 
ance was occasionally found, it was not sufficiently general to be 
called typical of this stage. 
In the first reduction division I succeeded in finding several cases 
of multipolar spindles, as Murbeck (1902, p. 7) has also reported. The 
two reduction divisions follow one another in rapid succession, form- 
ing a tetrad, whose members are oriented to each other after the 
manner of the four quadrants of a somewhat elongated sphere (see 
Murbeck, fig. 16). A similar arrangement is figured by Bornet (1864) 
in Cymodocea, and is not uncommon in the monocotyledons in general. 
During the two reduction divisions I was able in several cases to 
count eight chromosomes, which is, therefore, the reduction number, 
as Murbeck (1902) also found in Ruppia rostellata. 
In the study of the development of the pollen-grain, as in other 
structures, I found it of advantage to use a certain definite method 
of external measurement as an index to the stage of internal develop- 
ment. Thus, in the case of the pollen-grain, I chose the length of 
the grain, which, from its first formation in the tetrad to the mature 
condition, increases from about 175 w to about 550 w. Although 
these dimensions are subject to some variation, even in the same 
pollen-sac, yet they are fairly constant for the same period of growth. 
At the time of the formation of the tetrads the nucleus is in an 
approximately central position. Very soon after, or while the grain 
is still not much more than 175 w in length, the nucleus shows a 
position nearer to one end of the grain (PJ. XII, fig. 88), and a central 
zone of small starch grains has appeared. Almost immediately there- 
after one finds the nucleus at the end of the grain, the starch grains 
having become considerably larger and uniformly distributed (Pl. XI, 
fig. 89). A nuclear division now ensues (Fig. 90), and as a result, 
the small lenticular cell at the end of the grain, the generative cell, 
is formed (Fig. 92). 
