226 



BOTANT. 



numerous. 



The spore-cases are enclosed in rounded 

 "fruits" or receptacles which are 

 modified parts of leaves. 



422. The small spores, upon ger- 

 minating, produce a slight outgrowth 

 of a few cells (some of which de- 

 velop antherids and spiral anthero- 

 zoids), which is the extent of the 

 sexual plant. The large spores like- 

 wise produce a few-celled growth, 

 which is barely large enough to burst 

 and protrude beyond the spore-wall. 

 Archegones are developed upon these, 

 and from them, after fertilization, 

 the asexual stage of the plants is 

 produced. 



A few species of Pepperworts are spar- 

 ingly found in the United States. Some 

 have four-lobed leaves, as In the genus 

 Marsilia (Fig. 134), of which M. quadrifolia 

 occurs in New England, M. vestita and 

 others in the Mississippi valley and west- 

 ward ; Pilularia, with filiform leaves, is 

 represented by P. americana of the South- 

 west ; it is 3 to 4 centimetres high, and 

 grows in muddy places ; Azolla, contain- 

 ing 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 hithejto, are doubt- 

 less much more common than we now 

 consider them to be. 



Practical Studies. — (a) Collect several 

 different kinds of ferns, including the 

 underground portions as well as the leaves. Study the fibro- vascu- 

 lar bundles, stony tissue, and iibrous tissue iu the underground 

 Stem (Fig. 135). 



Fig. 134.— a Pepper- 

 wort (Marsilia salvatrix, 

 from Australia). Jc, the 

 creeping stem, bearing 

 the divided leaves, of 

 which b, b, are the ster- 

 ile, and /, /, the fertile, 

 parts (the so-called 

 fruits). One half the 

 natural size. 



