PART II: MORPHOLOGY AND LIFE HIS- 

 TORY OF REPRESENTATIVE PLANTS. 



CHAPTER XIX. 

 SPIROGYRA. 



197. Convenience in studying spirogyra. — 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 entirely ignorant of any 

 members of the lower groups. 



198. 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 perform- 

 ing 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. 



199. Conjugation of spirogyra. — Under certain conditions, 

 when vegetative growth and multiplication cease, a process of 

 reproduction takes place which is of a kind . termed sexual 



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