MORPHOLOGY AND LIFE HISTORY OF REPRE- 

 SENTATIVE PLANTS. 



CHAPTER XV. 



SPIROGYRA. 



219. In our study of protoplasm and some of the processes of 

 plant life we became acquainted with the general appearance of 

 the plant spirogyra. It is now a familiar object to us. And in 

 taking up the study of representative plants of the different 

 groups, we shall find that in knowing some of these lower plants 

 the difficulties of understanding methods of reproduction and 

 relationship are not so great as they would be if we were entire- 

 ly ignorant of any members of the lower groups. 



220. Form of spirogyra. — We have found that the plant 

 spirogyra consists of simple threads, with cylindrical cells 

 attached end to end. We have also noted that each cell of the 

 thread is exactly alike, with the exception of certain "hold- 

 fasts " on some of the species. If we should examine threads in 

 different stages of growth we should find that each cell is capable 

 of growth and division, just as it is capable of performing all the 

 functions of nutrition and assimilation. The cells of spirogyra 

 then multiply by division. Not simply the cells at the ends of 

 the threads but any and all of the cells divide as they grow, and 

 in this way the threads increase in length. 



221- Multiplication of the threads. — In studying living material of this 

 plant we have probably noted that the threads often become broken by two of 

 the adjacent cells of a thread becoming separated. This may be and is accom- 



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