jConjugation 

 tube 



Zygote 



Vegetative ceil 



Beginning of conjugation tube .i ..-^-^ , 



Hugh Spencer 



CONJUGATION IN SPIROGYRA 



In threads of Spirogyra lying close together, the cells put forth projections, which grow 

 toward their opposites. The projections dissolve at the point of contact, and the 

 protoplasm of one cell moves entirely into the opposite cell. The fused protoplasm 

 becomes a single spore with a thick wall 



location for resuming life's activities. Or we may think of them as the "germs" 

 which initiate new plants and animals to replace the life that has come to an end. 



Cell Fusion Like the cells of growing tissues, spores result from a divid- 

 ing up of existing protoplasm. We think of spores as highly specialized rep7V' 

 ductwe cells, for they "do" nothing unless there is a chance to start growing a 

 fresh line of protoplasm; and when a spore does start a new individual, it at 

 once goes out of existence itself. Now, in addition to extending life by growth 

 or by spores, most plant and animal species reproduce by a method that is in 

 a sense the reverse of cell-division. Under certain conditions two distinct cells 

 unite, or fuse, into one cell. This new cell that results from such a joining is 

 then the first cell of a new growth. 



In the common pond scum spirogyra, the individual cells all look alike; 

 and they are almost independent of one another, although they cHng together 

 in long threads. Each cell has chlorophyl and manufactures its ov/n organic 

 food. In the course of a few sunny days in the spring, a pond may become 

 covered over with millions of the green threads. In darkness and at low tem- 

 perature, as the threads become entangled in the water, two cells lying op- 

 posite each other may put forth budlike outgrowths which meet end to end. 

 The cell-walls at the point of contact dissolve, and the protoplasm from one 



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