288 
METHODS IN PLANT HISTOLOGY 
After the stage shown in Figure 101A has appeared, it is necessary 
to collect every day until the stage shown in Figure 101D is reached. 
If collections are made at intervals of 3 or 4 days, the most interesting 
stages, like the cutting off 
of the ventral-canal cell, 
fertilization, and the first 
divisions of the nucleus of 
the oospore, may be missed 
altogether. It should be. 
mentioned that all the 
ovules of a cone will be in 
very nearly the same stage 
of development; conse¬ 
quently, it is worth while 
to keep the ovules from 
each cone separate. 
Stages like that shown in 
Figure 102 are rare in mis¬ 
cellaneous collections, but 
if ovules from each cone 
are kept separate and this 
figure is found, the rest 
of the ovules from that 
cone will be likely to show 
some phase of this interest¬ 
ing mitosis. 
Thuja and Juniperus 
are good types to illustrate 
the archegonium complex 
and the large, highly or¬ 
ganized male cells. In 
Thuja a series from the 
appearance of archego¬ 
nium initials to young 
embryos may be collected between June 10 and June 20. In 
Juniperus pollination occurs late in May and fertilization takes place 
12J months later. The megaspores are formed late in April and 
Fig. 103 .—Pinus Banksiana: photomicrograph of young 
embryos teased out by the method described in the text; 
from a preparation by Dr. J. T. Buchholz; Cramer contrast 
plate; 16-mm. objective; no ocular or Abb6 condenser; 
camera bellows, 75 cm.; safranin filter; arc light; exposure, 
17 seconds. Negative by Miss Ethel Thomas. X54. 
the development of the 
weeks. 
female gametophyte occupies about 6 
