108 SITVIBIONTICISM AND THE ORIGIN OF SPECIES 



Red sea is due to Cyanophyceae) are diffused throughout 

 the cytoplasm. The Cyanophyceae do not contain a dis- 

 tinct nucleus. In the central part of the cell, there is a 

 material that has nuclear staining properties and is usually 

 considered a nucleus, but it lacks a nuclear membrane in 

 most cases. The Cyanophyceae together with the bacteria 

 {Schizomycetes) constitute a plant division, the Schizo- 

 phyta, in the opinion of most botanists. In other words, 

 the blue-green algae are similar and closely related to the 

 bacteria. 



The origin of the chloroplasts in algae and higher plants 

 has interested botanists for many years. Schimper ('85) 

 first suggested the continuity of chloroplasts in de- 

 velopment. He beheved that chloroplasts arise from 

 preexisting chloroplasts by a process of division. Guillier- 

 mond ('21) and others have shown that chloroplasts origi- 

 nate from mitochondria in ontogeny by a process of trans- 

 formation. The various stages of transformation have 

 been so clearly illustrated by Guilhermond that very httle 

 doubt exists in regards to the accuracy of his observations. 

 His discoveries have been confirmed by a large number of 

 investigators, and this method of plast-formation has been 

 introduced into text books. Not only are chloroplasts 

 formed in this manner, but other kinds of plasts (chromo- 

 plasts, amyloplastids, leucoplasts) are also formed from 

 mitochondria by a process of differentiation. The chloro- 

 phyl in these plastids is not apparent in the mitochondrial 

 stage of development, but appears in later differentiation. 

 In many instances a pyrenoid is associated with the chloro- 

 plast. The shape of the plast is somewhat variable. It is 

 usually circular in outhne, but in Euglena viridis (a proto- 

 zoan) it is star-shaped, while in Microglena pnnctifera 

 (also a protozoan) it is in the form of two elongated rods. 



It is evident from the data that have just been given, 

 that chloroplasts and other plasts of the higher green plants 



