SPERMATOPHYTES—GYMNOSPERMS 
275 
northern Florida, all stages are 2 or 3 weeks later. If one is so for¬ 
tunate as to get cones of Ceratozamia, the sperms should be found from 
the last week in June through the second week in July. 
Oogenesis.— The ovules of the Cycads and Ginkgo are very large, 
and, when mature, thin sections cannot be cut by any method yet 
discovered. In younger stages it is not difficult to get good sections 
of the entire ovule. Slabs should be cut from two sides of the ovule 
to facilitate fixing and infiltration. During free nuclear stages in the 
endosperm, and even during earlier stages in the formation of walls, 
care must be taken that the slabs may not cut into the endosperm, 
or even too near to it; for the endosperm is so turgid that it may 
even break out, and, at least, will be distorted. Even after the ovule 
approaches its full size, it can be cut entire, until the stony layer 
begins to harden. Paraffin sections of the entire ovule, cut 15 to 
20 \x thick, and stained rather lightly in safranin, gentian-violet, 
orange, make very instructive preparations. When the fresh ovule 
can no longer be cut easily with a razor, it is not worth while to try 
to cut it in paraffin. Interesting preparations may be made by 
cutting from the median longitudinal portion of the ovule a slab 
about 5 mm. thick. The slab should be fixed, washed, dehydrated, 
and cleared in xylol. It should then be kept in a flat-sided bottle. 
Such a preparation shows the integument, micropyle, nucellus with 
its beak, pollen tubes, the stony and fleshy layers, general course 
of vascular bundles, and the female gametophyte with its archegonia. 
For thin sections of the archegonia, a cubical piece with an edge 
of 6 or 8 mm. should be cut from the top of the endosperm with 
a very sharp, thin blade. The slightest pressure upon the archegonia 
will ruin the preparations. 
Chromo-acetic-osmic acid (1 g. chromic acid, 2 c.c acetic acid, 
and 1 c.c. of 1 per cent osmic acid to 100 c.c. of water) is a good 
fixing agent for all stages in oogenesis. During the free nuclear stage 
and early wall stage in the female gametophyte, some plasmolysis 
is to be anticipated. Hot alcoholic corrosive sublimate-acetic acid 
sometimes fixes these stages with less distortion. 
Sporophyte.—During the period of simultaneous free nuclear 
division, which follows the fertilization of the egg, the mitotic 
figures are quite striking and are easily stained (Fig. 96). 
After the embryos begin to grow down into the endosperm, 
oblong pieces containing the embryos should be cut out. 
