PTERIDOPHYTES—EQUISETALES 
253 
for demonstration, put a few on a slide, moisten a little, and watch 
the movements under the microscope. Strobili of other species, like 
E . fluviatile and E. hiemale, contain a large amount of silica and, 
consequently, only the younger stages cut well in paraffin. Hydro¬ 
fluoric acid damages the cell contents more or less. In species like 
these, all stages in the development are found in a single season. 
The Gametophytes. —The spores of Equisetum germinate as soon 
as they are shed, but, like all spores with a considerable amount of 
chlorophyll, they do not long retain the power of germination. A 
comparatively small percentage will germinate a week after shedding, 
and after a month, there may be no germination at all. There is 
no difficulty in growing prothallia to maturity and securing stages 
in the embryo, if fungi or blue-green algae do not appear and ruin 
the cultures. Use Costello’s method for fern prothallia, as described 
on page 263. Consult also a paper by Dr. Elda Walker. 1 This 
paper corrects some previous misconceptions in regard to gameto¬ 
phytes of Equisetum , gives a full account of the gametophyte of 
E. laevigatum, and also directions for finding gametophytes as they 
occur in nature. 
The prothallia fix well in chromo-acetic acid. The younger stages 
may be stained in iron-alum, haematoxylin and mounted in Venetian 
turpentine. The older stages, even of E. arvense , are too large for 
such mounts. E. laevigatum has prothallia a centimeter in diameter. 
For the development of antheridia, the blepharoplast, and the 
development of the sperm, fix in Flemming’s weaker solution and 
stain in iron-haematoxylin. The sperm of Equisetum is the largest 
in Pteridophytes. 
1 Botanical Gazette, 71:378-391, 1921. 
