166 CRYPTOGAMOUS OR FLOWERLESS PLANTS. [SECTION 17. 



the plant itself or its essential organs, that they have to be elaborately 

 described in separate books and made subjects of special study. 



504. Nevertheless, it may be well to try to give some general idea of 

 what Algae and Lichens and Fungi are. Linnaeus had them all under the 

 orders of Algae and Fungi. Afterwards the Lichens were separated ; but 

 545 546 547 



of late it has been made most probable that a Lichen consists of an Alga 

 and a Fungus conjoined. At least it must be so in some of the ambiguous 

 forms. Botanists are in the way of bringing out new classifications of the 

 Thallophytes, as they come to understand their structure and relations 

 better. Here, it need only be said that 



505. Lichens live in the air, that is, on the ground, or on rocks, trunks, 

 walls, and the like, and grow when moistened by rains. They assimilate air, 

 water, and some earthy matter, just as do ordinary plants. Algae, or Sea- 



550 



551 



552 



weeds, live in water, and live the same kind of life as do ordinary plants. 

 Fungi, whatever medium they inhabit, live as animals do, upon organic mat- 

 ter, — upon what other plants have assimilated, or upon the products of 



Fig. 545, 546. Two plants of Riccia natans, about natural size. 547. Magnified 

 section of a part of the frond, showing two immersed spore-cases, and one emptied 

 space. 548. Magnified section of a spore-case with some spores. 549. Magni- 

 fied spore-case torn out, and spores; one figure of the spores united; the other of 

 the four separated. 



Fig. 550. Branch of a Ohara, about natural size. 551. A fruiting portion, 

 magnified, showing the structure; a sporocarp, and an antheridium. 552. Outlines 

 of a portion of the stem in section, showing the central cell and the outer or 

 cortical cells. 



