PTERIDOPHYTA. 205 
smaller than it is in the true ferns, indicating a tendency 
towards its disappearance. 
Two genera, Ophioglossum, Adder-tongues proper, and Botrychi- 
um, the Moonworts, are represented in the United States by ten or 
eleven species. 
431. The Pepperworts (Order Rhizocarpee) are small 
aquatic or semi-aquatic plants, producing spores of two 
kinds, viz., small ones (microspores) which are very numer- 
ous, and large ones (macrospores) which are less numerous. 
The spore-cases are ertclosed in rounded “ fruits” or recep- 
tacles which are modified parts of leaves. 
432. The small spores, upon germinating, produce a 
slight outgrowth of a few cells (some of which develop 
antherids and spiral antherozoids), which is the extent of 
the first stage. The large spores likewise produce a few- 
celled growth, which is barely large enough to burst and 
protrude beyond the spore-wall. Archegones are devel- 
oped upon these, and from them, after fertilization, the 
leafy stage of the plants is produced. 
A few species of Pepperworts are sparingly found in the United 
States. Some have four-lobed leaves, asin the genus Marsilia (Fig. 
115), of which M quadrifolia occurs in New England, M. vestita and 
others in the Mississippi valley and westward; Pilularia, with filiform 
leaves, is represented by P. americana of the Southwest; it is 2 to 4 
centimetres high, and grows in muddy places; Azolla, containing 
minute, moss-like, floating plants, is represented throughout the 
United States by A. caroliniana. These interesting plants, which 
should be sought for more than they have been hitherto, are doubt- 
less much more common than we now consider them to be. 
Practical Studies.—(a) Collect several different kinds of ferns, in- 
cluding the underground portions as well as the leaves. Study the 
fibro-vascular bundles, stony tissue, and fibrous tissue in the under-_ 
ground stem (Fig. 116). 
