250 Causes and Course of Organic Evolution 



vided in any species T\qth motile processes or cilia. But though 

 passive the entire process resembles, and is apparently the 

 evolving forerunner of, swarmspore formation in higher algae. 



Our knowledge is still imperfect and fragmentary as to the 

 exciting causes that start formation of these different types 

 of cell. But all indications decisively point to changing envir- 

 onal stimuli as the causes for starting varying energizing modi- 

 fications — either increased or decreased in energy amount — 

 which by long continued action have slowly molded the or- 

 ganism. 



We can now investigate another and more complicated 

 question that directly pertains to the subject-matter of this 

 chapter. Phillips (35: 303) states that in an Oscillaioria studied 

 by him, and which he repeatedly demonstrated to the writer, 

 an apparent breaking dowTi of adjacent cell walls and union 

 of adjacent cell contents occurred, the diffused chromatin of 

 each cell seeming to participate largely in the process. Phillips 

 says regarding it: '* Whether this fusion should or should not 

 be looked upon as a form of sexuality is problematical, how- 

 ever, for the reason that spores are sometimes formed in Oscil- 

 laria, as in Cylindrospermum and other Cyanophycese, by the 

 transformation of only one cell, but even here we find the same 

 passing of chromatin into the single spore cell from the adjoin- 

 ing, or, as they might be termed, the nurse cells." 



While we would not attach too great an importance to these 

 results till they are carefully and repeatedly verified or dis- 

 proved, they at least suggest that commencing sexuality is 

 associated with forming or evolving chromatin substance, a 

 position that is strongly suggested by all studies made on 

 nucleate organisms. 



So for the simple Cyanophycese it can be said that sexuality 

 is absent or possibly rarely indicated, and that multiplication 

 is effected by some mode of vegetative division of a cell or 

 of a chain of cells. In the higher thread forms, where chro- 

 matin formation and aggregation can be traced, several modi- 

 fications of asexual di\dsion are developed, that correspond 

 to akinete, aplanospore, and endospore formation in higher 

 algae. These seem in all cases to be due to rather rapid and 

 pronounced changes in environal conditions, that have grad- 

 ually modified lines of energy distribution, and so have modified 

 the protoplasmic substance. It is suggested that a possible 

 primitive sexual fusion may occur in a few genera between 

 adjacent cells, though as yet the question requires fuller veri- 

 fication. 



