Chap. IX. WHEAT. 335 



as the Neolithic period, cultivated no less than ten cereal 

 plants, namely, five kinds of wheat, of which at least four are 

 commonly looked at as distinct species, three kinds of barley, 

 a panicum, and a setaria. If it could be shown that at the 

 earliest dawn of agriculture five kinds of wheat and three of 

 barley had been cultivated, we should of course be compelled 

 to look at these forms as distinct species. But, as Heer has 

 remarked, agriculture even at the Neolithic period, had already 

 made considerable progress ; for, besides the cereals, peas, 

 poppies, flax, and apparently apples, were cultivated. It may 

 also be inferred, from one variety of wheat being the so-called 

 Egyptian, and from what is known of the native country of 

 the panicum and setaria, as well as from the nature of the 

 weeds whicli then grew mingled with the crops, that the lake- 

 inhabitants either still kept up commercial intercourse with 

 some southern people or had originally proceeded as colonists 

 from the South. 



Loiseleur-Deslongchamps *^ has argued that, if our cereal 

 plants have been greatly modified by cultivation, the weeds 

 which habitually grow mingled with them would have been 

 equally modified. But this argument shows how completely 

 the principle of selection has been overlooked. That such 

 weeds have not varied, or at least do not vary now in any 

 extreme degree, is the opinion of Mr. II. C. Watson and 

 Professor Asa Gray, as they inform me ; but who will pretend 

 to say that they do not vary as much as the individiuxl plants 

 of the same sub-variety of wheat? We have already seen 

 that pure varieties of wheat, cultivated in the same field, ofier 

 many slight variations, which can be selected and separately 

 propagated ; and that occasionally more strongly pronounced 

 variations appear, which, as Mr. Shirrefi" has proved, are well 

 worthy of extensive cultivation. Not until equal attention 

 be paid to the variability and selection of weeds, can the 

 argument from their constancy under unintentional culture 

 be of any value. In accordance with the principles of 

 selection we can understand how it is that in the several cul- 

 tivated varieties of wheat the organs of vegetation differ so 

 little ; for if a plant with peculiar leaves appeared, it would 



*^ ' Les CertSales,' p. 94. 



