PLANT HYBRIDIZATION BEFORE MENDEL 207 



Darwin and Mendel, and the single experiments of Henslow, also 

 with Digitalis^ and of MacFarlane with a number of other species, 

 constitute the only quantitative measurements made upon hybrid 

 cases prior to 1900. The data are few, but are historically inter- 

 esting. They show the intermediate condition in the F^ generation 

 in respect to length and width of the organs measured, (p. 320.) 

 By Focke's time (1881) the details regarding the behavior of 

 hybrids had sufficiently accumulated so that he was able to say : 



"Our knowledge concerning the fertilization of plants has noticeably- 

 extended during recent decades, so that we are no longer in a position 

 to group the facts together, as has been customary, under a few general 

 standpoints. The multifariousness of the phenomena in organic nature is 

 enormously greater than one has thus far been accustomed to assume." 

 (p. 446.) 



Focke had distinctly the physiological rather than the morpho- 

 logical point of view regarding hybrids and hybridization, and 

 was not bound by wooden or stereotyped conventions of thought 

 regarding the systematic relations of species. 



"Taken as a whole, it is correct, that the groups of forms do not as a 

 rule very well admit of being delimited according to their sexual be- 

 havior. The degrees of morphological and physiological differences cor- 

 respond to one another frequently somewhat exactly, yet there are ex- 

 amples in which this is absolutely not the case." (p. 448.) 



Again he expresses a plastic point of view in this regard, in 

 the following words : 



"One will do well not to judge the morphological relations between 

 two plant forms according to their physiological behavior and vice versa. 

 It is a question in every case of- determining the facts, but not to force 

 them into a definite mould. 



"Under all circumstances, from the beha'vior of hybrids, one may only 

 with great care be able to draw conclusions concerning the specific like- 

 ness or unlikeness of the parental forms." (p. 449.) 



The fact that, as a rule, the nearer the systematic relationship 

 becomes, the more readily what are called "species" cross, was 

 naturally sufficiently recognized by Focke. 



"Two essentially different species can scarcely ever completely mu- 

 tually fertilize each other." (p. 457.) 



"Many hybrids, especially those between unlike parent species, are, as 

 stated, unfruitful ; the most show a diminished, a few an almost normal 

 fertility." (p. 457.) 



"A delimitation of genera in such a manner that all species which are 

 able to furnish hybrids among one another may be placed in the same 

 genus, would be extremely unnatural. On the other hand, it is not far- 



