108 STUDY OP COMMON PLANTS. 



known, and have received such, popular names as "sea- 

 mosses," "flowers of the sea," etc. 



Attractive, however, as the study of these different 



groups with their peculiarities is to the special student, it 



is chiefly in the green alsrse that the interest 



Green algae. •' i ? i • • i 



Evolution of centres when we seek to discover the ongnials 

 g or p an s. ^^^^^ which the higher forms of plants have been 

 derived. If we assume that Vaucheria, for example, stands 

 as a representative of certain primeval plants that have per- 

 sisted until the present time, retaining their primitive sim- 

 plicity of structure, while others have gradually taken on 

 the complicated form and structure with which we are 

 familiar in higher plants, we shall have a starting-point 

 from which to proceed in our effort to trace the successive 

 stages of evolution of plant life on the globe. The point 

 of departure is a plant consisting of a single cell, but with 

 the capacity for cell-division, reproducing itself by the sep- 

 aration of buds, or their equivalent, and by sexually pro- 

 duced oospores. As we proceed to higher groups, we shall 

 find that these same facts repeat themselves. Cell division 

 proceeds farther, differentiation of tissues and organs takes 

 place with corresponding division of labor, and the parts 

 concerned in reproduction become more conspicuous and 

 of more complicated structure, but the essentials are all 

 represented in Vaucheria and the simple plants with which 

 it is associated. Our knowledge of the actual history is 

 extremely limited, but the possibility of rendering it more 

 complete by the discovery of new facts and the right inter- 

 pretation of those already known, gives point and direction 

 to much of the biological investigation of the present day. 



