Organic Characters Composite 15 



2. The Similarity of the Differences Betzveen Species 



and Between Organs 



The comparison of species with the organs of a single 

 individual leads us to quite similar conclusions as does 

 the comparison of species with each other, for the dif- 

 ferences between the organs can be traced back, in the 

 same way, to various combinations of individual heredi- 

 tary qualities. 



Even the simplest observation teaches us this. Just 

 as chlorophyll is lacking in some species it is also lacking 

 in single organs and tissues of higher plants. The red 

 coloring matter of flowers is limited to certain plant 

 species, and in these again to definite organs. Tannic 

 acid, etherial oils, and like substances, where present, 

 show a local distribution. Calcium oxalate is lacking in 

 most ferns and grasses, and on the other hand in the roots 

 of many species rich in calcium. The same is true, ap- 

 parently, of morphological attributes. I need not cite ex- 

 amples, for it will certainly be granted that a very close 

 agreement exists between the manner in which the or- 

 gans of a single plant differ from each other and the dis- 

 tinction between different species. Both depend upon 

 varying combinations and a varying selection from a 

 great range of given factors. 



A series of phenomena, which we may summarize un- 

 der the name dichogeny, leads to similar conclusions. I 

 mean all those cases where the nature of an organ is not 

 yet decided during the early stages of its development, 

 but may yet be determined by external influences. Thus, 

 under normal conditions, the runners of the potato-plant 

 form at their tips the tubers, but on being exposed to 

 light, or when the main stem has been cut off, they de- 



