Spermatophytes Gymnosperms 



249 



which is so turgid that distortion would be sure to result. 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 fj, 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 zylol. It should then be kept in a flat-sided bottle. 



FIG. 87. Zamia floridana: photomicrograph of a small portion of the proembryo 

 showing simultaneous free nuclear division safranin, gentian- violet, orange; Cramer 

 contrast plate; 4mm. objective; ocular X4; yellowish-green filter; Camera bellows, 

 50cm.; exposure, 6 seconds. X413. 



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 arche- 

 gonia. 



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. 



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. 87). 



