GROUPS OF PLANTS. 



II 



as CONJUGATION, and the zygospore is called a resting spore. It 

 should be explained that certain cells, as well as spores, may lie 

 dormant for a period, as during the winter season or at otlier- 

 times, when the conditions are unfavorable to growth, and then 

 renew their activities, these being known as " resting cells." 



Vaucheria (Fig. 8) is another common green alga which 

 may also be selected as showing the habits of this group of 

 plants. The plant has a branching thallus and lives in shallow 



Fig. 8. Vaucheria sessilis. A, sporangium from which the multiciliate zoospore is 

 escaping; B, resting zoospore; C, D, germinating zoospores with growing point (s); E, 

 plant showing root-like organ of attachment (w), spore from which the plant is develop- 

 ing (sp), F, showing in addition two oogonia (og) and an antheridium (h). After Sachs. 



water or on moist earth, being attached 'to the substratum by 

 means of delicate root-like processes sometimes spoken of as 

 rhizoids (Fig. 8, iv). In the thin layer of protoplasm lying near 

 the wall are numerous nuclei and small oval chromatophores. 

 Numerous oil globules are also found in the protoplasm, and cal- 

 cium oxalate crystals may occur in the cell-sap. 



Vaucheria furnishes an example of a plant whose interior is 

 not segmented by cell walls. In other words, the cavity within 

 the outer or enclosing membrane is continuous, and such a plant 



