214 ESSENTIALS OF BOTANY 



From the types discussed it is evident that in the case 

 of yeast and Pleurocoocus a cell is an individual plant. In 

 Cladophora and many other thread-like genera either one 

 cell of a filament or a straight or branching row of similar 

 cells is an individual. In the mosses, ferns, and still more 

 highly developed types the plant is composed of many 

 layers of cells, which have assumed various forms to fit 

 them for their several duties. 



270. Series of Spore-Plants. — The spore-plants are 

 grouped in three grand divisions, or series, as follows : ^ 



Series I. Thallophytes? One-celled or several to many- 

 celled plants of very simple organization, usually without 

 separate root, stem, and leaves, always without fibro-vas- 

 cular bundles. 



Series II. Bryophytes, or liverworts and mosses. Small 

 plants which sometimes consist merely of a nearly flat mass 

 of cellular tissue sometimes have a leafy stem, but are 

 always without true roots or fibro- vascular bundles. The 

 method of reproduction is of a far more advanced char- 

 acter than in Series I. 



Series III. Pteridophytes, or ferns, horsetails, and club 

 mosses. Plants, some of them small, others large, with 

 true roots, stems, and leaves, and with fibro-vascular bun- 

 dles (although the vessels have not exactly the structure of 

 those in seed-plants). The method of reproduction is still 

 more advanced than in Series II. 



1 See p. 210. This section should not he studied in detail until the discus- 

 sion ol pteridophytes (Chapter XXVII) is completed. 



2 This is a rather miscellaneous group and the name is somewhat misleading, 

 as some bryophytes also have a plant body consisting only of a flat thaUus. 



