THE FIRST PLANT HYBRIDIZER 83 



Vries had narrowly escaped discovery at the hands of their 

 predecessors. There was lacking only the numerical exact- 

 ness of a Mendel or the clear-sighted analysis of a De Vries 

 to bring to light the rule governing the splitting of hybrids. 



By a hybrid we understand an organism produced by the 

 crossing of two distinct species or varieties of plant or animal, 

 i, e,, an organism which has an individual of one species or 

 variety as its mother and an individual of a different species 

 or variety as its father. At times and by certain naturalists 

 a distinction has been made between the offspring of a species 

 cross and that of a variety cross, the term hybrid being 

 limited to the progeny of a species cross, and the term mon- 

 grel being used to designate the progeny of a variety cross. 

 But it has been found quite impossible to distinguish species 

 from varieties sharply, for Darwin showed that varieties may 

 be only incipient species, and that no definition can be 

 framed of variety which will not also include species and 

 vice versa. Accordingly at present we use the terms species 

 and variety in a relative sense only. The differences which 

 exist between species are supposed to be either more numer- 

 ous or greater in degree than those which exist between 

 varieties. The terms to the majority of biologists imply 

 nothing more than this. If we cannot distinguish species 

 from varieties, it is obvious that we cannot distinguish the 

 products of a species-cross from the products of a variety- 

 cross, and so at present all cross-bred offspring, whether of 

 species or varieties, are called hybrids. The same law of 

 splitting applies to all, as we shall see. 



The pioneer plant hybridizer was Joseph (Gottlieb) Kol- 

 reuter (1733-1806) who between the years 1760 and 1766 

 carried out the first series of systematic experiments in plant 

 hybridization which had ever been undertaken. The more 

 important features of Kolreuter's work have been thus 

 summarized by Lock, pp. 150-155. 



These experiments not only established with certainty for the first time 

 the fact that the seeds of plants are produced by a sexual process com- 

 parable with that known to occur in animals, but also led to a knowledge 



