56 



EVOLUTION OF PLANTS 



third order, the Characese, is made up of very peculiar 

 plants of doubtful affinities. 



THE SIPHONED 



This order contains a good many types differing a 

 good deal among themselves and showing in some cases 



a high degree of special- 

 ization, 

 from the 

 forms in 

 complete 



differ 



They 



other green 

 the almost 

 absence of 

 division walls within 

 the plant body, although 

 they can hardly with 

 propriety be considered 

 as strictly unicellular 



FIG. 11. Part of a plant of Caulerpa Since the protoplasm 



plumaris, one of the Siphonese, show- , -, T 



ing external differentiation into stem, Contains a large number 



root, and leaf in a non-cellular plant ; n p rniP l P i 'TUp WJant 

 x, the growing point ; r, rootlets. 



may be a simple tubular 



filament, or it may be extensively branched and form a 

 body of considerable size showing a remarkable degree 

 of external differentiation, actually mimicking the struct- 

 ure of the higher plants in the development of stem, 

 leaf, and root (Fig. 11) ; but even in such cases the 

 hollow cavity of the thallus is undivided by partition 

 walls. The wall is lined with a protoplasmic layer in 

 which are imbedded the numerous nuclei and chloro- 

 plasts. The division of the nuclei, of course, is not 

 accompanied, as in most cells, by the formation of a 

 division wall. 



