ELECTIVE AFFINITY. . 499 



comprised within certain limits, varying with the particular 

 species. Very early experiments in hybrid fecundation before 

 the expansion of the blossom seldom succeed, and no impreg- 

 nation will take place with strange pollen when the stigma has 

 arrived at such a state that its own pollen is not able to 

 fecundate the whole ovary. In any case, however, there is no 

 difference in the hybrid types resulting from the experiment. 

 3. The stigma, when ready for the reception of the pollen, 

 secretes in every case a greater or less quantity of moisture, 

 which doubtless acts an important part in the process of 

 fecundation. In certain cases it may be thought necessary to 

 apply some fluid to the stigma for the better retention and 

 development of the pollen grains. For this purpose the honey 

 secreted by the flower, or that of some allied species, may be 

 used without any modification of the produce. Oily fluids, 

 such as various purer oils, also have been used with success, 

 though not uniformly. Water, on the contrary, is generally 

 unfavourable, though in some water-plants, in strict analogy 

 with the observations of Spallanzani on the fecundation of the 

 ova of certain aquatic reptiles, it has clearly no injurious if not 

 a beneficial influence. 3. In some cases, especially in those 

 where hybridisation is rare, outward conditions, such as 

 increased temperature, predispose plants for hybrid impreg- 

 nation, and cultivation in general is favourable to this end, as it 

 is to the production of deviations from a normal condition. 

 Varieties are usually far more disposed to mix than the species 

 fi-om which they are derived, and hence the great difficulty of 

 keeping our most valuable vegetables pure and genuine. Of 

 all genera Calceolaria seems to present the greatest tendency 

 to hybridise ; the pure species unite with the utmost facility, 

 and their hybrids are aU fertile and disposed to fresh 

 admixture. 



He also attaches great importance to what he calls elective 

 AFFINITY, or the preference which the stigma has for the poUen 

 of one plant rather than of another. He found that when 

 the stigma is dusted at the same time, or within certain limits, 

 with its own pollen in sufficient quantity, and that of some 

 other species, the latter is whoUy inert, and the result is plants 



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