8o PLANT-BREEDING 



which had been selected anew in the fields during the pre- 

 ceding season. The book-keeping embraces the complete 

 botanical description of each new sort, from its germination 

 until the time of the harvest, with all the details required 

 for the controlling of its constancy and uniformity, and for 

 the study of all those quahties upon which the introduction 

 into general agriculture will ultimately depend. 



I have purposely left the hybrids out of consideration 

 until this time. In the beginning we saw that, although uni- 

 formity is the prevailing rule for the progeny of a single 

 mother plant, exceptions regularly occur. These have been 

 ascribed to the effect of accidental crosses. Until some time 

 ago it was assumed that crosses were of common occurrence 

 only with rye, the other grains fertihzing themselves. But 

 experience has shown that this is only an average rule, and 

 that everywhere in the fields accidental crosses may occur. 

 Their progeny arc, of course, hybrids, and these may spht 

 in the next generation according to distinct laws, as studied 

 for cereals by Rimpau and other investigators. Any char- 

 acter which was different in the two parents of the cross, 

 may thus split in the progeny of the hybrid, and in this 

 way new combinations of characters may arise. Experience, 

 however, shows that in ordinary fields almost all possible 

 combinations may be met with, and it is to be presumed 

 that at least the greater number of them are due to crosses 

 in previous and, perhaps, in long-forgotten years. In the 

 following generations, these new combinations of character 

 may become fixed in part of the progeny of the hybrids, and 

 it is a well-known fact that such constant races are the ordi- 

 nary results of natural and artificial crosses. Hence, we may 

 conclude that some, and perhaps many, of the types which 

 may be selected and isolated in the fields and which prove 

 to be constant races must be of hybrid origin. 



Whenever such an original hybrid is found in the field 



