72 ON THE INTERCROSSING [CHAP. IV. 



species ; for if a plant's own pollen and that from another species 

 are placed on the same stigma, the former is so prepotent that it 

 invariably and completely destroys, as has been shown by Gartner, 

 the influence of the foreign pollen. 



When the stamens of a flower suddenly spring towards the 

 pistil, or slowly move one after the other towards it, the con- 

 trivance seems adapted solely to ensure self -fertilisation ; and no 

 doubt it is useful for this end : but the agency of insects is often 

 required to cause the stamens to spring forward, as Kolreuter has 

 shown to be the case with the barberry ; and in this very genus, 

 which seems to have a special contrivance for self-fertilisation, it 

 is well known that, if closely-allied forms or varieties are planted 

 near each other, it is hardly possible to raise pure seedlings, so 

 largely do they naturally cross. In numerous other cases, far from 

 self-fertilisation being favoured, there are special contrivances 

 which effectually prevent the stigma receiving pollen from its own 

 flower, as I could show from the works of Sprengel and others, as 

 well as from my own observations : for instance, in Lobelia 

 fulgens, there is a really beautiful and elaborate contrivance by 

 which all the infinitely numerous pollen -granules are swept out of 

 the conjoined anthers of each flower, before the stigma of that 

 individual flower is ready to receive them ; and as this flower is 

 never visited, at least in my garden^ by insects, it never sets a 

 seed, though by placing pollen from one flower on the stigma of 

 another, I raise plenty of seedlings. Another species of Lobelia, 

 which is visited by bees, seeds freely in my garden. In very many 

 other cases, though there is no special mechanical contrivance to 

 prevent the stigma receiving pollen from the same flower, yet, as 

 Sprengel, and more recently Hildebrand, and others, have shown, 

 and as I can confirm, either the anthers burst before the stigma is 

 ready for fertilisation, or the stigma is ready before the pollen of 

 that flower is ready, so that these so-named dichogamous plants 

 have in fact separated sexes, and must habitually be crossed. So 

 it is with the reciprocally dimorphic and trimorphic plants pre- 

 viously alluded to. How strange are these facts ! How strange 

 that the pollen and stigmatic surface of the same flower, though 

 placed so close together, as if for the very purpose of self- 

 fertilisation, should be in so many cases mutually useless to each 

 other ? How simply are these facts explained on the view of an 

 occasional cross with a distinct individual being advantageous or 

 indispensable ! 



If several varieties of the cabbage, radish, onion, and of some 

 other plants, be allowed to seed near each other, a large majori 

 of the seedlings thus raised turn out, as I have found, mongre' 

 for instance, I raised 233 seedling cabbages from some plants of 

 different varieties growing near each other, and of these only 76 



me 



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