98 Elementary Species 



of course not applicable to the wheat of Jersey 

 alone. The common cultivated sorts of wheat 

 and other grains were mixtures then as they 

 are even now. Improved varieties are, or at 

 least should be, in most cases pure and uniform, 

 but ordinary sorts, as a rule, are mixtures. 

 Wheat, barley and oats are self -fertile and do 

 not mix on the field through cross-pollination. 

 Every member of the assemblage propagates it- 

 self, and is only checked by its own greater or 

 lesser adaptation to the given conditions of life. 

 Eimpau has dealt at large with the phenomenon 

 as it occurs in the northern and middle parts of 

 Germany. Even Rivett's " Bearded wheat, " 

 which was introduced from England as a fine 

 improved variety, and has become widely dis- 

 tributed throughout large parts of Germany, 

 has kept itself pure. It is found mingled al- 

 most anywhere with the old local varieties, 

 which it was destined to supplant. Any lot of 

 seed exhibits such impurities, as I have had 

 the opportunity of observing myself in sowings 

 in the experimental -garden. But the impurities 

 are only mixtures, and all the plants of 

 Rivett's " Bearded wheat," which of course 

 constitute the large majority, are of pure blood. 

 This may be confirmed when the seeds are col- 

 lected and sown separately in cultures that can 

 be carefully guarded. 



