Nichols, A morphological study of Juniperus communis var. depressa. 219 
chromatic elements being beaped together in a compact mass which 
lies close to the nuclear membrane. Tbe cytoplasm of tbe cell 
appears more or less alveolar, and in it are imbedded numerous 
minute starch grains. The megaspore mother cell is slightly larger 
than the microspore mother cell, measuring about 35 /u x 20 /u, 
while its nucleus has a diameter of about 17 fx. 
Tetrad formation takes place about April 20 th . The first 
divisionof the mother cell nucleus, as observed by Noren (1907), 
gives rise to two nuclei containing the haploid number of chromo- 
somes. The spindle of this division is represented in figs. 61 and 
67. In the latter figure it will be seen that a cell plate has been 
formed, but a permanent membrane is rarely if ever laid down 
between the daughter nuclei. In this respect the heterotypic divi¬ 
sion of the megaspore mother cell resembles that of the microspore 
mother cell. Frequently a protoplasmic membrane separates the 
two nuclei, but often theylie free in the cytoplasm of the mother 
Fig. 2. 
Longitudinal section through young ovule about two weeks after pollination. 
Micropyle closed. X 66- 
cell (fig. 63). Both daughter nuclei become more or less com- 
pletely reorganized, but as a rule only the lower one of the two 
reaches a resting stage. In such cases the latter alone undergoes 
the homotypic division, and as a result there is usually produced 
a group of three cells (fig. 67), only two of which are morpho- 
logically megaspores. Where both nuclei divide, a true tetrad is 
formed. Figs. 64—66 represent instances in the species studied 
where both daughter nuclei are undergoing the homotypic division, 
and where four potential megaspores are thus being developed. 
It will be seen that the two spindles may lie either side by side 
or in Tandem’. No especial attention was given to the formation 
of these spindles, but fig. 64 shows a multipolar diarch similar to 
that noted by Miss Ferguson (1904, fig. 142) in Pinus. 
Noren (1907) States that he has never observed a case 
where more than one embryo sac has developed within a single 
nucellus.' The writer, however, was fortunate enough to secure 
one preparation in which three megaspore mother cells had under- 
