CLASSIFICATION OF FERNS. 21 



ish upon old rotten logs, tan, &c. They have a 

 peculiar jelly-like form, and are capable of slow 

 motion, absorbing their nourishment, as they pro- 

 ceed, from the substance on which they live. They 

 are not yet well enough understood to be definitely 

 placed in the system of classification. Passing to 

 the Fungi and Algce, we observe that these are two 

 classes of plants possessing certain parallel char- 

 acters of development : thus the lower Alga have 

 certain characters in common with the lower Fungi; 

 while the higher Fungi and Algcz, though vastly 

 more developed than the lower ones, have similar 

 features, each to each. This relates particularly 

 to their methods of producing fruit. It has there- 

 fore been proposed that they should be considered 

 to be two groups, parallel and equally advanced, 

 called the colored (Alg<z) and the colorless (Fungi). 

 This brings us to the Lichens, which unite the last 

 two groups in their organization. 



The Lichens are now considered by the most emi- 

 nent botanists to belong rather, to the Fungi than 

 to any other class. Their nature is thus stated by 

 Sachs : " There can no longer be any doubt that 

 the lichens are true fungi, but distinguished by a 

 singular parasitism. Their hosts are algae, which 

 grow normally in damp places, but not actually in 

 water. The fungi (the lichen-forming fungi) them- 

 selves are not found in any other form than as 

 parasites on algae ; while the algae which are at- 



