ON THE NATURE OF MITOCHONDRIA 461 
The presence of these primordial organisms in the beginning of 
evolution established the conditions essential for the develop- 
ment of those higher forms that require organic material for 
sustenance. It is not difficult to conceive the rdle that the 
primordial chlorophyl-bearing organisms played in the modus 
operandi of early evolution. Concerning themselves with the 
production of starch, the most important of the early food ma- 
terials, they undoubtedly assumed the roéle of food factories 
preparing the way for the evolution of higher life. 
The simplest organisms containing chlorophyl are bacteria 
or bacteria-like organisms. These organisms are generally called 
the blue-green algae. Campbell (99), Thom (712), Osborne 
(17), and other investigators, however, maintain that they 
are more closely related to bacteria than to algae. Regardless 
of their relationship, whether with the bacteria or with the algae, 
the fact remains that chlorophyll is one of the oldest specialized 
materials of living matter. 
It is in harmony with known biological behavior to conceive 
of chloroplasts not as organs developed in the cytoplasm of higher 
plants, but to look upon them as bacteria or bacteria-like organ- 
isms that accepted the leisure of a symbiotic partnership in the 
struggle for existence. In exchange for the nourishment sup- 
plied to it by the host plant, the invading symbiont furnishes an 
indispensable product to the host organism. It is obvious 
that if this interpretation coincides with reality, then the chloro- 
plast is an example of absolute symbiosis. 
The presence of-chloroplasts in certain animal cells makes 
the foregoing hypothesis all the more alluring. It is true, that 
in some of these animal cells the chlorophyl-bearing bodies are 
unicellular algae that have been ingested by the host organism. 
This fact, however, serves to demonstrate the possibility that 
certain animal celis are so chemically constituted that algae 
may live within their cytoplasm with apparent impunity. The 
possibility also suggests itself that unicellular chlorophyl-bearing 
organisms may develop a symbiotic relationship with some ani- 
mals and that the products of the chlorophyl-bearing organisms 
may be essential to the sustenance of the animal cell. 
