50 OUR NATIVE FERNS AND THEIR ALLIES. 



group; that the second like the first contains plants with a 

 highly organized structure; that the third is like the first two 

 in including plants with a distinct leafy axis, but differs in pos- 

 sessing a less complicated structure; while the last differs from 

 all the others in having no distinction of stem and leaves. To 

 bring out these and other characters more fully, and at the 

 same time to indicate some hints of the leading subdivisions of 

 these great groups of plants, will necessitate a more technical 

 and tabular arrangement. 



1 26. Tiie Thallophytes include the lower forms of vege- 

 tation whose plant-body varies from a unicellular condition, 

 through filamentous forms to a more or less highly differ- 

 entiated thallus. While some forms, especially among the 

 higher algae, assume the habit of a leafy-stemmed plant, none 

 attain to a true differentiation into stem and leaves. The 

 thallophytes are most simply divided on a purely physiological 

 basis into two main groups * : 



1. Algce which develop chlorophyll. 



2. 7^«;/^/which are parasitic or saprophytic colorless plants. 

 127. The Alg^ comprise the following groups : 



1. Cyanophyce^. (Blue-green algae, nostocs, etc.) 



2. DlATOMACE^. (Diatoms, secreting a siliceous Covering.) 



3. CHLOROPHYCE.B.t (Green algae.) Consisting of four 



well-marked groups : 

 [a) Proiococcoidea. (Green slimes, volvox, water-net.) 

 {b) CotijugatcE. (Desmids, Spirogyra, etc.) 

 {c) Siphonece. (Bladder-plants, green felts, etc.) 

 {d) Confervoidea:. (Sea-lettuce, water- flannel, etc.) 



* The sexual system of classification frequently adopted in this country can- 

 not be niaiiitained among the fungi, and even among the algae is at points 

 very unsatisfactory. Moreover it groups together forms that have no near 

 relation to each other and cannot be regarded as a natural system. It is 

 further to be doubted if the group commonly known as Protophytes can be 

 maintained on any rational grounds. 



t The Chlorophyceae include by far the greater part of the fresh-water 

 algae, though quite a number of the group are marine. The brown and red 

 alga? of the two following groups make up the most conspicuous marine 

 forms, 



