18 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



in the physical condition of a "gel" rather than a "sol" as in 

 the nerve cell, the distribution of the mitochondria is unaltered 

 by centrifuging (Key). There is no reason to believe that the 

 mitochondria themselves are different. At any rate, where the 

 method is apphcable (i.e., in egg cells) the mitochondria are 

 heavier than protoplasm, in which respect they conform to what 

 we know of phosphatids and differ sharply from oils and neutral 

 fats, which rise to the surface and float instead of being thrown 

 down. 



Granting that the specific gravity of mitochondria is 

 greater than that of the cytoplasm of the cell, such a cir- 

 cmnstance would not constitute evidence that they are 

 related to phosphatids merely because the latter are heavier 

 than cytoplasm. Regards the probabiUty that the mito- 

 chondria may be different in different varieties of cells, 

 Cowdry ('18, p. 85) remarks ''In some varieties of cells the 

 constitution of the mitochondria apparently differs, slightly 

 but noticeably, from that of the mitochondria in other cells, 

 though in cells of the same kind their composition is very 

 constant." The staining reactions of mitochondria when 

 the Giemsa stain and the Kull method are used, demonstrate 

 clearly that the mitochondria of a single cell are not all 

 alike. 



(6) Mitochondria act as solutes for various substances. They 

 are often pigmented and assume the most brilliant hues. Pre- 

 nant (Asvandourova, 1913, p. 293) has actually styled them 

 "chromochondria" on this account. This solution of other 

 materials in mitochondria is particularly frequent in plant cells. 

 It may or it may not be significant from the point of view of their 

 constitution. 



The evidence here does not appear to have any specific 

 bearing on a phospho-lipin-albumin constitution. 



(7) There seems to be a certain correspondence between varia- 

 tions in the histological picture of mitochondria and the variations 



