148 Causes and Course of Organic Evolution 



unexpected, and as now presented they may possibly suggest 

 to others a revisal or modification of their views on this subject. 



It was previously stated (p. 63) that the organic chemist 

 has already recognized and named about 50,000 compounds 

 that are either naturally present in organisms, or are obtained 

 from them artificially in the laboratory. Amongst so large 

 a number, the possibilities for new combinations and for molec- 

 ular changes in such complex and condensed laboratories as 

 plant and animal cells might well be regarded as enormous. 

 But, while it seems undoubtedly true that many of these — let 

 us roughly say 5000 at least — are actually produced in living 

 cells, the great majority of them are closely related compounds 

 of various chemical series, which differ from each other only 

 in the replacement of one or a few atoms or radicals, for 

 another, in a highly complex molecule. Given therefore the 

 formation of any one of a definite chemical series, as say grape 

 sugar in the glucose group, the formation of the other members 

 of the series would probably be a gradual but easy effort on 

 the part of the organism. 



The definitely recognized and named constituents of animal 

 tissues, moreover, often are identical with, or closely allied 

 to, those of plants; in rarer cases constituents are peculiar, 

 so far as we know, to one of the two great living groups. We 

 shall therefore for convenience consider plant and animal cell 

 contents together. 



But, in considering the possible origin or distribution of the 

 organic bodies, an important question at once presents itself, 

 which has not apparently received due consideration. It is 

 the following. Confining our attention meanwhile only to 

 plants as a field of study, even cursory examination shows 

 that many constituents encountered amongst the simplest 

 Caryota seem to be again lost or obliterated, only to reappear 

 higher up in the plant scale. Thus the red pigment of Chlor- 

 ococcum seems to be identical Tvith that of many other uni- 

 cellular algae or algoid spores, though in the adult plants that 

 these spores may form the pigment entirely disappears from 

 view, as in Ulothrix zonata^ etc. But it again reappears in 



