U3 a Nutrition of Multicellular 

 Plants 



HOLOPHVTIC nutrition became dominant 

 in the plant kingdom dining an early evolu- 

 tionary period, and as multicellular species 

 developed they gained greater efficiency by a 

 division of labor among the cells. Thus 

 gradually the specialized tissues and organs 

 of the modern higher plants came into being. 



MULTICELLULAR ALGAE 



All early primitive plants lived under 

 water, and the aquatic environment puts 

 little premium upon the de\elopment of 

 specialized parts. Natural bodies of water 

 contain adequate amounts of carbon dioxide, 



oxygen, and inorganic salts, so that every 

 cell of a submerged plant can absorb these 

 foods on an individual basis. Hence — as 

 might be expected — the degree of differenti- 

 ation among the cells of the green algae has 

 not been very great. 



Perhaps the commonest type of cell dif- 

 ferentiation among nonmotile green algae is 

 the modification ol some of the cells to form 

 organs of attachment. In some filamentous 

 algae, a single cell at the basal end of the 

 filament is specialized as a rhizoid (or hold- 

 fast) that attaches the filament to the soil or 

 rock at the bottom of the water (Fig. 13-1). 

 This specialized cell is modified in shape and 



Fig. 13 

 tiation. 

 a pond 



236 



CHLOROPLAST 



1. Young filament of Ulofhrix, a filamentous green alga, showing a slight degree of cellular differen- 

 Normally this plant grows in a more or less vertical position attached to some object on the bottom of 

 or stream. 



