CHAPTER NINE. 

 CONJUGATION. 



1. Review. Let us bring together the kinds of 

 reproduction we have studied thus far. In some forms we 

 have seen the whole parent divide into two offspring, each 

 one-half as large as the original parent. In others we 

 have seen the whole parent divide into many, small 

 spore-like offspring. Yet others put forth smaller bodies 

 which grow into new individuals without exhausting the 

 mother organism. Still others have special organs in 

 which many minute, single-celled spores are produced 

 and from which the spores escape without the destruction 

 of the parent. 



In many of these cases the offspring begin at once to 

 grow into the adult. Some of them, however, may rest 

 days or months before they begin to develop. All of 

 them have the power to develop directly without any 

 special stimulation other than from heat, moisture, food, 

 and so forth. 



2. Offspring That May Unite. We have purposely 

 omitted description of an interesting thing that sometimes 

 takes place even in many of the plants and animals 

 mentioned above, side by side with what we have already 

 described. In some of the fresh water algae (as Ulothrix, 

 a simple filamentous plant) the contents of the cells under 

 certain conditions divide into many motile spore-like 

 bodies. Some of these may swim around for a while and 

 then settle down and germinate into the filamentous form 



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