Method of Origin of New Species and Structures 421 



represent but one species (viz., Antennaria plantaginifolia) , has 

 been found to include a dozen, all perfectly distinct, permanent, 

 and recognizable by good observation; the Brambles and some 

 Grasses have been claimed to include not dozens of species but 

 hundreds; and the Hawthorns of America have already been 

 described to the number of over a thousand, with no end to the 

 trouble as yet. The same thing is true also of cultivated plants, 

 and strikingly so of the grains. A field of Indian Corn, for ex- 

 ample, has been found to consist not of one species, as we used to 

 suppose, but of dozens of biotypes, or elementary species, crossing 

 and hybridizing greatly it is true, but capable of separation and 

 ultimate pure breeding each by itself. It is important to remem- 

 ber, however, that the fact of the existence of these elementary 

 species is quite independent of the question as to their origin; and 

 many of those who have had most to do with their discovery 

 doubt whether they have arisen by mutation, though de Vries, of 

 course, believes that they did. 



There is one other great name associated with evolution, even 

 though somewhat indirectly, and that is Mendel, whose dis- 

 coveries in the particular field of heredity are exerting a profound 

 influence upon present-day evolutionary thought. We have 

 already discussed his work in our chapter on Reproduction, and 

 need only summarize here the points of importance to our im- 

 mediate subject. They are these: — 



First, each individual organism, animal or plant, is an aggre- 

 gate, or mosaic, as it were, of a definite number of characters 

 each of which is represented by a determiner or unit in the germ 

 cells from which it has developed. These characters are thou- 

 sands in number in the higher organisms, fewer in the simpler, and 

 include all kinds of features of structure, form, size, color, etc. 

 Thus eye-color in man, and the number of rows of grains on an 

 ear in Corn, are such unit characters. 



Second, every germ cell, whether egg-cell or sperm-cell, con- 

 tains one complete set of units capable of reproducing all the 



