The Lower Plants 55 



in the form of zoospores, which are identical in 

 structure with the cells of Volvox. 



Multicellular Algae. While a good many of the 

 lower algae remain unicellular, more of them are 

 multicellular organisms. Among the simplest of 

 these multicellular algae are the various " pond- 

 scums," those soft, foamy green masses so 

 often seen floating on stagnant water. These 

 plants consist of chains of entirely similar cells 

 floating free in the water. Others of these 

 low algae, such as the one shown in Fig. 4, B, are 

 attached, and the basal cell may develop root- 

 like outgrowths so as to form a definite organ of 

 attachment. These plants often multiply by means 

 of zoospores, little, naked, free-swimming cells 

 closely resembling the cells of Volvox. After a 

 short period of activity, these zoospores settle down, 

 develop a cell wall, and thus for a short period as- 

 sume a typically unicellular condition. By repeated 

 divisions, this cell then gives rise to the character- 

 istic filament, or cell row. It will be seen, then, that 

 in its development the plant passes successively 

 through the free, motile stage, and the stationary 

 unicellular condition, before it finally attains its 

 adult multicellular state. 



Photosynthetic Organs in Algae. From these 

 simple beginnings there may be traced many inter- 

 mediate stages leading up to the branched or broad 

 flattened bodies which distinguish the more compli- 

 cated types of algae. This increase in the complex- 



