276 
METHODS IN PLANT HISTOLOGY 
After the cotyledons appear, useful preparations may be made by 
dissecting out the entire embryos, which may be fixed in chromo- 
acetic acid, washed, stained in eosin or in Delafield’s haematoxylin, 
placed in 10 per cent glycerin, and mounted by the Venetian turpen¬ 
tine method. Since the suspensors become long and irregular, each 
embryo should be placed in a separate dish, lest the suspensors be¬ 
come entangled and broken. 
Fig. 96. —Zamia floridana: photomicrograph of a small portion of a proembryo showing 
simultaneous free nuclear division. Fixed in chromo-acetic-osmic acid and stained in safranin, 
gentian-violet, orange. Cramer contrast plate; Spencer 4-mm. objective, N.A. .65; ocular X4; 
yellowish-green filter; camera bellows, 50 cm.; arc light; exposure, 6 seconds. Negative by Miss 
Ethel Thomas. X413. 
After the stony layer becomes hard, it is better to use a small 
fret saw for opening the ovule. Before the embryo has pushed down 
into the endosperm, the ovule should be sawed in two transversely. 
The endosperm and nucellus can then be picked out and treated as 
desired. After the tip of the embryo reaches the middle of the endo¬ 
sperm, the ovule should be sawed open longitudinally. 
GYM NOSPERMS—GINKGOALES 
From the standpoint of technic, the Ginkgoales, now represented 
only by Ginkgo biloba, are less difficult than the Cycadales, but the 
difficulties are somewhat similar. 
The Vegetative Structures— The adult stem is harder to cut than 
Pinus, but good sections should be secured by boiling in water and 
soaking for a few days in glycerin. Transverse sections of the “ spur ” 
shoots are easily cut. They have a comparatively large pith and 
narrow zone of wood, thus contrasting sharply with a long shoot of 
the same diameter, which has a small pith and wide zone of wood. 
