CELLULAR PLANTS. LICHENS. 107 



CRYPTO'GAMOUS PLANTS. 



Division of Cryptoga'mia. (See table on page 102.) 



24. Crypto' gamous plants are constituted exclusively, or 

 chiefly of cells, and during the first period of their growth, or 

 even throughout their existence, are unprovided with vessels and 

 stigmas ; they also differ from phanero' gamous plants in their 

 mode of propagation, for their multiplication always takes place 

 without the aid of various reproductive organs, analogous to 

 stamens and pistils, and is effected by the division or by the 

 development of sporules, bodies which resemble the seeds of 

 ordinary plants, but have no protecting envelope like a pericarp, 

 nor a depot of nutritive matter similar to the albumen, or to 

 cotyledons. We divide these plants into two groups; cellular 

 plants properly so called, and semi-vascular plants. 



25. CELLULAR PLANTS properly so called are composed ex- 

 clusively, and at all periods of their existence, of cellular tissue, 

 which forms a homogeneous mass and is rarely green ; their 

 forms, which are very various, do not at all resemble those of 

 ordinary plants ; we can distinguish in these plants neither roots 

 nor organs similar to stems or leaves, and absorption seems to 

 take place throughout the whole extent of their surface. When 

 their tissue is membranous and flat, we give the part thus con- 

 stituted the name of thallus, and when branched and spread out, 

 it constitutes what is called a frond or frons. The sporules are 

 sometimes naked, sometimes contained in one or more membran- 

 ous sacks which seem to be ordinary cells. 



26. This group is divided into three natural families; Lichenes, 

 Fungi, and Alga3. 



27. LICHENS are perennial plants which grow upon the trunks 

 of trees, on rocks, or on the surface of the ground, and are com- 

 posed of a thallus (possibly from the Greek, thaleia, the bloom- 

 ing one) having the appearance of filaments, of foliaceous mem- 

 branes or hardened pulve'rulent crusts. This thallus consists of 

 two layers, one external or cortical, variously coloured, but never 

 green ; and an internal or medullary, which often contains green 

 matter and gives origin to young plants, either by the division of 

 its tissue or by the production of spores (from the Greek, spora, 



24. What are the general characters of crypto'gamous plants? How do 

 they differ from phanero'gamous plants ? What are sporules ? How are 

 crypto'gamous plants divided ? 



25. What are the general characters of cellular plants ? What is a 

 thallus? What is a frond ? . 



26. How are cellular plants divided ? 



27. What are lichens ? What is the character of the thallus in lichens f f 



