THE BLUE-GREEN ALG^E 27 



from the Bacteria in that no forms bear flagella. Per- 

 haps we had better regard them as a side-line in the 

 evolution of plant forms. Their possession of chloro- 

 phyll indicates ability to manufacture carbon com- 

 pounds, but it is doubtful whether they are completely 

 independent of provided organic food. The mode of 

 occurrence of some of them, at any rate, points to the 

 possibility of a partially parasitic or saprophytic habit. 

 One thing is certain, they are an extremely simple and 

 primitive type of plants. 



One might say that this chapter is arrayed in motley, 

 for we have assembled for description some hetero- 

 geneous types of life-forms. From an undoubted animal 

 form we progressed to the Myxomycetes, which may be 

 animal or plant, or both; then we proceeded to deal 

 with undoubted plants, the Bacteria and Blue-Green 

 Algse, whose origin and relations are extremely doubtful. 

 The forms dealt with are of great simplicity, and one 

 feature in regard to them all is the absence of sex. The 

 probability is that the earliest forms of life, both plant 

 and animal, reproduced asexually, and that sex was a 

 later development one fraught with the utmost im- 

 portance. 



