330 METHODS IN PLANT HISTOLOGY 



and fleshy layers, general course of vascular bundles, and the female 

 gametophyte with its archegonia. 



If living cones should be available, it would be worth while to try 

 Gourley's basic fuchsin method. Under the liquid, cut the ovule off, 

 with a httle of the sporophyll. After 14 hours, fix the ovule in absolute 

 alcohol, changing once or twice. After clearing, keep it in equal parts 

 of xylol and carbon disulphide. 



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. Since the slightest pressure upon the archegonia 



Fig. lU.—Zamia floridmm: photomicrograph of a small portion of a proembryo showing simul- 

 taneous 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. 0.6.5; ocular X4; yellowish- 

 green filter; camera bellows 50 cm. ; arc light; exposure, 6 seconds. Negative by Miss Ethel Thomas. 

 X41.3. 



will ruin the preparations, it is better not to cut closer to the arche- 

 gonia than 2 mm. After the material is in 85 per cent alcohol, the sides 

 of the cube can be shaved off with a safety razor, making the piece 

 much smaUer to cut, so that as many sections can be mounted on 2 

 slides as on 3, without the trimming. 



Chromo-acetic-osmic acid (1 g. chromic acid, 2 c.c. acetic acid, and 

 6 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 antici- 

 pated. Hot alcoholic corrosive sublimate-acetic acid sometimes fixes 

 these stages with less distortion. 



Sporophyte.— During the period of simultaneous free nuclear divi- 

 sion, which follows the fertilization of the egg, the mitotic figures are 

 quite striking and are easily stained (Fig. 114). 



