224 N - H - COWDRY. 



One point more. The close resemblance of mitochondria, 

 amounting almost to identity in both plants and animals, may 

 indicate a common ancestral form possessing mitochondria. It 

 is a general assumption that plants antedate animals, and it 

 seems significant that among the lower plants, and not in the 

 lower animals, we find groups in which mitochondria have not 

 been detected. I have particularly in mind the Alga, for in this 

 interesting group some forms contain mitochondria and others 

 do not (M. and Mme. Moreau, '15, p. 730). The absence of 

 mitochondria is interpreted in various ways. Some think that 

 the large chloroplast takes over their function (Guilliermond, 

 '13, p. 86) and it is possible that the mitochondrial substance 

 may be present in an invisible diffuse condition. There is every 

 reason to believe that the possession of formed mitochondria is 

 an attribute even more primitive than the possession of a fully 

 formed nucleus, which, unlike the mitochondria, has gradually 

 assumed a more specialized character. Yeast plants in which 

 the presence of a nucleus is debated (Macallum, '99, p. 67) 

 unquestionably contain them (Janssens and Helsmortel, '13, 

 p. 452), and there are indications that some bacteria also have 

 mitochondrial material. This is beside the question, however, 

 because the Saccharomycetes and Schizomycetes are probably 

 degraded forms. We can look upon the ancient line of evolution 

 as passing through forms closely resembling some of the Alga 

 of the present day which are devoid of mitochondria, into similar 

 forms possessing mitochondria and which gradually acquired 

 fully developed nuclei in addition. From these nucleated alga- 

 like organisms containing mitochondria, the higher plants and 

 the whole animal kingdom gradually evolved. They stood at 

 the parting of the w T ays. The geological record, incomplete 

 as it is, seems to indicate that the algee are the oldest of plants; 

 those of the present day being the lineal and comparatively 

 unaltered descendants of the most ancient ones. It is surprising 

 that mitochondria should persist without great modification 

 through all the storm and stress of millions of years of evolution 

 during which everything else changed except perhaps the primi- 

 tive living homogeneous ground substance. As they were in the 

 beginning so they are now, on the crest of both animal and plant 



