PLANTS OULTIVATED FOR THEIR SEEDS. 895 



jectural -knowledge. I will state what I take to be the sum 

 of this, because it leads to certain probable indications. 



I remark first that maize is a plant singularly un- 

 provided with means of dispersion and protection. The 

 grains are hard to detach from the ear, which is itself 

 enveloped. They have no tuft or wing to catch the wind, 

 and when the ear is not gathered by man the grains fall 

 still fixed in the receptacle, and then rodents and other 

 animals must destroy them in quantities, and all the 

 more that they are not sufficiently hard to pass intact 

 through the digestive organs. Probably so unprotected 

 a species was becoming more and more rare in some 

 limited region, and was on the point of becoming extinct, 

 when a wandering tribe of savages, having perceived its 

 nutritious qualities, saved it from destruction by culti- 

 vating it. I am the more disposed to believe that its 

 natural area was small that the species is unique ; that is 

 to say, that it constitutes what is called a single-typed 

 genus. The genera which contain few species, and 

 especially the monotypes, have as a rule more restricted 

 areas than others. Palaeontology will perhaps one day', 

 show whether there ever existed in America several species \ 

 of Zea, or similar Graminse, of which maize is the last ' 

 survivor. iNow, the genus Zea is not only a monotype, 

 but stands almost alone in its family. A single genus, j 

 Euchlcena of Schrader, may be compared with it, of which 

 there is one species in Mexico and another in Guatemala ; 

 but it is a quite distinct genus, and there are no inter- 

 mediate forms between it and Zea. 



Wittmack has made some curious researches in order 

 to discover which variety of maize probably represents 

 the form belonging to the epoch anterior to cultivation. 

 For this purpose he has compared ears and grains taken 

 from the mounds of North America with those from Peru. 

 If these monuments offered only one form of maize, the 

 result would be important, but several different varieties 

 have been found in the mounds and in Peru. This is not 

 very surprising ; these monuments are not very ancient. 

 The cemetery of Ancon in Peru, whence Wittmack 

 obtained his best specimens, is nearly contemporary with 

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