CEYPTOGAMOUS OR FLOWEKLESS PLANTS. 



505 



sporangia from the under side : these open variously, but are not 

 four-valved. Elaters with two spiral fibres. 



977. Sul)Ord. Jungermanniacea!. Frondose or mostly foliaceous 

 plants ; with the sporangium dehiscent into four valves, and' the 

 spores mixed with elaters. 



Class V. Thallophytes. 



Vegetables composed of parenchyma alone, forming a mass or 

 stratum (thallus, 109, 727), or consisting of a congeries of cells, or 

 even of separate cells, never exhibiting a marked distinction into 

 root, stem, and foliage, or into axis and leaves. 



978. Ol'di Hellenes (Zdchens) form the highest grade of this lower 

 series. They consist of flat expansions, which are rather crustaceous 

 than foliaceous ; while some are nearly pulverulent. In several the 

 vegetation rises into a kind of axis, or imitates stems and branches ; as 

 in the Cladonia coccinea, which abounds on old logs (Fig. 1327) ; or 

 in Cladonia rangiferina, the Reindeer Moss ; also in Usnea, where 

 it forms long, gray tufts, hanging from the boughs of old trees in our 

 Northern forests. Lichens are never aquatic, but grow on the ground, 

 on the bark of trees, or on exposed rocks, to which the proper rock- 

 Lichens adhere by their lower surface, with great tenacity, while by 



FIG. 1319. Steetzia Lyellii, with the young fructification still included in the tubular peri- 

 anth, 1820. Dehiscent sporangium of a Jungermannia, on its fruit-stalk, with some of the 

 leaves at its base, magnified enough to exhibit its cellular structure. 1321. Two elaters from 

 the same (a, iu an entire state ; &, with only the threads remaining), and some spores, highly 

 magnified. 



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