THE SIMPLER ORGANISMS 



65 



8 





The form of the plant body is much influenced by the 



manner of cell division. When 

 the cells separate completely at 

 division, the plant remains per- 

 manently unicellular. AV h e n 

 elongate cells divide transverse- 

 ly, and remain attached, the 

 linear aggregate results: when 

 they divide lengthwise, such 

 rafts as those of Scenodesmus 

 (fig. 46) and of many diatoms 

 H' ^ TkT result. When the planes of di- 



^ /^ vision of the cells of a linear ag- 



gregate become oblique, cutting 

 off from the cells prolonged api- 

 cal angles, the filaments become 

 branched as in Cladophora (fig. 

 47). When no division planes 

 are formed, only the nucleus, 

 but not the cytoplasm dividing, 

 overgrown multinucleate cells 

 are formed. One such t3^pe, 

 that is enormously overgrown 



Fig. 46. Miscellaneous algae, 

 further illustrating types of 

 cell form and arrangement, a, 

 Clathrocystis, actively divid- 

 ing; b, Scenodesmus acutus; c, 

 Scenodesmus caudatus; d, Sele- 

 nastrum; e, Hydrodictyon, /, 

 Cosmarium; g, Staurastrum; 

 h, Euastrum. 



in long irregular interlacing fibres, is 

 Vaucheria, the green felt — an alga 

 that is found abundantly on wet soil 

 in greenhouses. 



One observes in studying the algae 

 that the transition from unicellular 

 to multicellular forms is very gradual. 

 First, there are multitudes of single, 

 completely independent cells. Then 

 there are those algae that consist 



Fig. 47. Cladophora 

 s , a branch; 

 t, a tip from the 

 same, to show cell 

 arrangement. 



