52 Causes and Course of Organic Evolution 



Blue-green Algae. The writer would here refer the reader 

 who desires greater detail to such monographic accounts as 

 those of Zopf (29), Hansgirg (30), Gomont (31), West (32), 

 and Tilden (33), specially also to the excellent condensed 

 description by Kirchner in " Pflanzenf amilien" (34). 



In structure each living cell is bounded by a mucilaginous 

 wall of material related to cellulose, as well as in some cases 

 an additional film related to cutin. Both of these, according 

 to Hegler, can resist chemical agents much as cutin does. 

 Within is a protoplasmic mass, that shows under 1000° mag- 

 nification a finely granular, but doubtless profoundly complex, 

 hereditary structure, that faitlifully hands down exact molec- 

 ular details to succeeding derivative cells. The outer spherical 

 or cylindric zone of this protoplasm usually has a semifoamy, 

 semireticular aspect, and this has the bluish green, brownish 

 green, or reddish green pigment distributed through its sub- 

 stance. Hence the entire outer zone has been called the chrom- 

 atophore. It is of interest to observe — alike in itself and in 

 its connection with animal cells — that this often includes small 

 masses of glycogen, which seem to be formed in the zone as a 

 carbohydrate food. Within, the clear protoplasm in some 

 cases fills the central part of the cell, but in the multicellular 

 and so more evolved thread-forms clear granules begin to 

 appear. These assume varying degrees of union and com- 

 plexity, until a loose open network or skein of chromatin is 

 formed (35: 296) which evidently is the evolving nucleus that 

 appears in perfected state in all the Caryota. Further, the 

 protoplasm of neighboring cells is often connected by delicate 

 tags that pass through the partition walls. 



While our physiological knowledge of the group is still too 

 imperfect to permit of important conclusions, Klitzing (36: 181) 

 has shown that movements toward or away from heat and 

 light are made by some, that suggest a sluggish response to 

 thermic and lumic stimuli. 



But a wide field exists for comparative physiological investi- 

 gation of the degree and rapidity of response to environal 

 stimuli, sho^Ti by the simplest and the most complex blue- 



