542 LIFE-HISTORIES 
reproduction is sometimes accomplished in ferns by the formation 
on various parts of buds which fall to the ground and take root 
(see Fig. 368). 
Filicinze in general agree with the ferns described in being ont 
goniate, vascular plants, forming true roots and stems, and having 
alternate leaves upon which are borne sporangia that discharge their 
spores without elaters. The number of species is reckoned at about 
3,000. 
193. The scouring-rushes (Class Equisetingz) are repre- 
sented in modern times only by comparatively small plants 
of the genus Equisetum (Fig. 369)—about 25 species— 
which, however, are closely related to numerous gigantic 
rush-like coal plants, typified by the genus Calamites 
(Fig. 277, 2). 
In Equisetum cross-fertilization is accomplished by having male 
and female gametophytes which, as shown in Figs. 370, 371, differ 
considerably from one another, the female being much the larger 
and suggesting somewhat by its pseudo-leaves the nurse-plant of a 
moss. The sporophyte differs remarkably from that of any fern in 
the comparatively great development of the stem. This is hollow 
except at the nodes, and performs nearly all the work of photosyn- 
thesis. 
The roots do not differ essentially from those of ferns, but 
the foliage leaves are reduced to toothed sheaths serving 
chiefly to protect the tender regions of the stem. The fibro- 
vascular bundles of the stem are arranged in a ring, and in 
some forms (mostly extinct) a cambium like that of higher 
plants is developed which gives rise to successive rings of 
tissue. Such additional material by which increase in thick- 
ness is accomplished takes the name of secondary tissue, to 
distinguish it from the primary tissue formed by the primary 
meristem. The epidermis is often so filled with silica or flint, 
as to render the plants useful for scouring metal, and this 
accounts for the popular name. Certain subterranean 
branches of the rhizoma (a, Fig. 369) may have their funda- 
mental tissue gorged with reserve food, and thus form tubers 
which feed new growth in spring, and may sometimes serve 
as a means of vegetative reproduction. Among the vertical 
branches there is often a differentiation into the purely 
vegetative and the purely reproductive. The latter terminate 
