CHAPTER XIV. 



THE PEOTOPHYTA. 



269. — The Protophytes are the lowest and simplest plants. 

 In many cases they are exceedingly minute, requiring the- 

 highest powers of the microscope for their study. For the 

 most part the cells are poorly developed ; the protoplasm 

 is frequently destitute of granular contents ; the nucleus is 

 wanting in many cases, and not infrequently there is either 

 no cell-wall, or only a poorly deyeloped one. The cells in 

 all cases have little or no coherence, and even when they are 

 united into loose masses, each cell retains nearly as much 

 independence as in the unicellular forms. The differentia- 

 tion of cell-form is very slight, even in those cases where 

 there is the greatest coherence of cells, and yet in some or- 

 ders certain cells of the filaments are uniformly larger than 

 the others, as the " heterocysts " of Nostoc, and the "basal 

 cells" of the filaments of Rivuluria. 



270. — No sexual organs are known, and whether the sex- 

 ual act occurs or not is somewhat doubtful. As, however, 

 we must not expect to find well-developed organs or as 

 distinct a sexual act in these simple organisms as in more 

 complex ones, it is possible that both exist in the group, 

 but have hitherto been overlooked or misunderstood. 



Their most common mode of reproduction is by fission, 

 and in only a few cases by internal cell-division. 



271. — The lowest Protophytes are destitute of chlorophyll,, 

 or any other coloring-matter, and in those orders in which 

 chlorophyll occurs it is usually associated with a blue or red 

 pigment. 



Many Protophytes exist in masses of a considerable size, 

 composed of large numbers of individuals imbedded in a. 



