PTEBIDOPHTTA. 205 



« 



smaller than it is in the true ferns, indicating a tendency 

 towards its disappearance. 



Two genera, Opliioglossum, Adder-tongues proper, and Botrychi- 

 um, the Moonworts, are represented in the United States by ten or 

 eleven species. 



431. The Pepperworts {Order Bhizocarpeoe) 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 enclosed 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 harely 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-Iobed leaves, as in 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. americaua of the Southwest; it is 2 to 4 

 centimetres high, and grows in muddy places; AzoUa, 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. 



PraeUeal 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). 



