THE AI/LE 



183 



to each other. The cells may either round themselves 

 off and separate immediately after each division, or 

 may remain grouped together for a few generations. 

 Sooner or later, however, they fall apart. The plant 

 forms small starch-grains in 

 the chloroplasts when exposed 

 to light. 



We have in Pleurococcus an 

 example of a typically unicel- 

 lular plant, in which the cells 

 lead a perfectly independent 

 life ; each individual cell, how- 

 ever, has the same structure 

 as in higher plants. Evidence 

 has recently been brought FIG. 77. Pleurococcus vulgaris. 



fnrwprrl fn chnw tVmt Phtirn ^> sin gl e ce ^ 5 n > nucleus; 



Drwara to snow wiau neuro- ^ chloroplastids. B, four 



COCCUS possesses Other means cells separating after division. 



of reproduction besides simple %$$> &?TSK 



Cell-division, and that it passes have just divided afresh. D, 

 \_ i_ J.T. ' i. tetrahedral group. Magnified 



through Other Stages of exist- 540 . (After Strasburger.) 



ence than that described. It 



is probable that the life-history is in reality a rather 

 complex one, but at present the whole of the facts have 

 not been made clear. 



R THE BBOWN ALG^E (Phceophycece) 



The brown Algae almost all of which are seaweeds, 

 are probably better known to the ordinary observer 

 than even the green group, owing to the large size 

 which many of them attain, and the extraordinary 

 abundance in which they occur on our coasts. In 

 dimensions and structure they present an even wider 



