SPERMATOPHYTES—GYMNOSPERMS 
285 
Oogenesis.—In Pinus Laricio the rudiment of the ovulate strobi- 
lus, which is to be pollinated in June, can be detected in the preceding 
October. The collection of this stage is very uncertain, because there 
seems to be no mark distinguishing buds containing ovules from buds 
which are only vegetative. By collecting numerous buds from the 
tops of vigorous trees which are known to produce an abundance of 
strobili, a few buds containing the desired stages may be obtained. 
In May, after the strobili break through the bud scales, material 
is easily collected. Up to the time of pollination the entire ovulate 
strobilus cuts easily in paraffin. Longitudinal sections of the cone at 
this time give good views of the bract and ovuliferous scale bearing 
the ovules. The integument is very well marked, and in the nucellus 
one or more sporogenous cells can usually be distinguished. As 
soon as the scales close up after pollination, the cone begins to harden 
and soon makes trouble in cutting. Even before the scales close up, it 
is better to cut a slab from opposite sides of the cone; after the scales 
close, it is almost a necessity. For sections of the whole cone, fix 
in formalin alcohol. Dr. Hannah Aase succeeded in cutting complete 
series of paraffin sections from cones of Pinus Banksiana more than 
2 cm. in length. She fixed them in formalin alcohol, and used pro¬ 
longed periods in dehydrating, clearing, and infiltrating. Land’s 
bichromate of potash and glue fixative was used in fixing the sections 
to the slide. Such series of sections of large cones were necessary for 
an investigation of the vascular anatomy. 
For a study of the ovule and the structures within it, better 
preparations will be obtained by carefully cutting off the pair of 
ovules from the scale. In free nuclear stages of the female gameto- 
phyte, which begin in the autumn, are interrupted by winter, and are 
completed in May, plasmolysis is likely to occur. After walls appear 
there is less danger. From the middle of May to the first of July 
collections should be made at intervals of two or three days, since 
during these six weeks the gametophyte completes the free nuclear 
stage and develops cell walls, the archegonium completes its entire 
development, the egg is fertilized, and the sporophyte may reach the 
suspensor stage. 
At the stages shown in Figure 101 B-D, it is a good plan to remove 
the female gametophyte with its proembryos from the ovule; but 
at the stages shown in Figures 10L4 and 102 the pollen tubes with 
their contents are rapidly working their way through the nucellus 
