SPERMATOPHYTES—GYMNOSPERMS 
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mother-cells at the top, it is very probable that longitudinal sections 
of the cone will yield the figures. If a drop of methyl green be 
allowed to run under the cover, it will enable one to see whether 
figures are present or not. When desirable cones are found, slabs 
should be cut from two sides, in order that the fixing agent may pene¬ 
trate more rapidly and that infiltration with paraffin may be more 
thorough. 
The later stages, showing the germination of the microspores, 
furnish better sections if the cones are cut transversely into small 
pieces about 5 mm. thick. It is very easy to get excellent mounts 
of the pollen just at the time of shedding, which, in Pinus Laricio 
in the vicinity of Chicago, occurs near the middle of June. Shake 
a large number of cones over a piece of paper, thus securing an 
abundance of material; slide the pollen off from the paper into a 
bottle half-full of water and shake a little to wet the pollen grains, 
because pollen of wind-pollinated plants is likely to be more or less 
shriveled at the time of shedding. A few minutes in water will 
make the pollen turgid. Fix in formalin-alcohol-acetic acid. If 
material is so abundant that you can lose much of it and still have 
plenty left, fix in chromo-acetic-osmic acid. Staining, especially 
the staining of mitotic figures, is likely to be more brilliant after 
fixing in the chromic series. However, most of the mitoses take 
place before the pollen is shed or after it reaches the nucellus. Infil¬ 
tration in the bath will not require more than 30 minutes. When 
the infiltration is complete, pour out into a paper tray or an imbedding 
dish, just warm enough to allow the pollen to settle to the bottom. 
A layer of pollen 3 mm. thick, with enough paraffin to make the cake 
about 5 mm. thick, will be satisfactory for cutting. Or, the paraffin 
may be poured out upon a piece of cold glass. Still another method 
is to leave the paraffin in a shell or vial during infiltration in the bath, 
and then let it cool in the bottle. After the paraffin is hard, break 
the bottle. Break the bottle carefully, cut off the lower portion of the ^ 
paraffin containing the pollen, mount it on a block in the usual man¬ 
ner, and trim away some of the paraffin so that two parallel surfaces 
will make the sections ribbon well. Sections should not be thicker 
than 5 m- Material in this stage shows a large tube nucleus, a some¬ 
what lenticular (generative) cell with a more deeply staining nucleus, 
and, lastly, two small prothallial cells quite close to the spore 
wall. The prothallial cells cannot always be detected at this stage, 
