308 



VARIATION OF PLANTS AND ANIMALS. [Ch. XXXVI. 



Gartner, in his work on the hybridisation of plants, has 



species which can be united with 



some 



unusual facility, will produce sterile hybrid^, while others 

 which are crossed rarely 



extreme difficulty 



exam 



different 



hybrids which are very fertile, as 



species of the genus DiantJius or pink. The same botanist 



repeatedly crossed the common red and blue pimpernels, 



Anagallis 



ensis 



and A. coerulea^ which, says Darwin, the 



best naturalists rank as mere varieties of one species, and 



sterile. These plants, besides their 



them 



distinctness in colour, differ slightly in the nervation of their 

 leaves and in the shape of their petals ; and botanists who 



im 



are specifically distinct, although scarcely any of them would 

 have come to such an opinion before the experiment of cross- 

 ing had been tried- 



Wieo:mann 



much as possible his mode of 

 bringing about these irregular unions among plants. He 

 often sowed parallel rows, near to each other, of the species 

 from which he desired to breed ; and, instead of mutilating, 

 after Kolreuter's fashion, the plants of one of the parent 

 stocks, he merely washed the pollen off their anthers. The 

 branches of the plants in each row were then gently bent 

 towards each other and intertwined; so that the wind, and 

 numerous insects, as they passed from the flowers of one to 

 those of the other species, carried the pollen and produced 



fecundation. 



When 

 in conveying 



busily many insects are engaged 

 from flower to flower, especially 



bees, flower-eating beetles, and the like, it seems a most 



matical problem 



it can happen that promiscuous 



alliances between distinct species are not perpetually oc- 

 curring. 



How continually do we observe the bees diligently em- 

 ployed in collecting on their hind legs the red and yelloAV 

 powder by which the stamens of flowers are covered, and 

 after passing from one flower to another, carrying it to 

 their hive for the purpose of feeding their young ! Ii^ 

 thus providing for their own progeny, these insects assist 





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