HYBRIDISM » 



sterility. Kolreuter makes the rule universal; but then 

 he cuts the knot, for in ten cases in which he found two 

 forms, considered by most authors as distinct species, 

 quite fertile together, he unhesitatingly ranks them as 

 varieties. Gartner, also, makes the rule equally universal; 

 and he disputes the entire fertility of Kolreuter's ten cases. 

 But in these and in many other cases, Gartner is obliged 

 carefully to count the seeds, in order to show' that there 

 is any degree of sterility. He always compares the maxi- 

 mum number of seeds produced by two species when first 

 crossed, and the maximum produced by their hybrid off- 

 spring, with the average number produced by both pure 

 parent-species in a state of nature. But causes of serious 

 error here intervene: a plant, to be hybridized, must be 

 castrated, and, what is often more important, must be se- 

 cluded in order to prevent pollen being brought to it by 

 insects from other plants. Nearly all the plants experi- 

 mented on by Gartner were potted, and were kept in a 

 chamber in his house. That these processes are often 

 injurious to the fertility of a plant cannot be doubted; 

 for Gartner gives in his table about a score of cases of 

 plants which he castrated, and artificially fertilized with 

 their own pollen, and (excluding all cases such as the 

 Leguminosae, in which there is an acknowledged difficulty 

 in the manipulation) half of these twenty plants had their 

 fertility in some degree impaired. Moreover, as Gartner 

 repeatedly crossed some forms, such as the common red 

 and blue pimpernels (Anagallis arvensis and coerulea), 

 which the best botanists rank as varieties, and found 

 them absolutely sterile, we may doubt whether many 

 species are really so sterile, when intercrossed, as he 

 believed. 



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