OBSERVATIONS UPON MULING AMONG PLANTS. 



163 



An important deduction arises from these exceptional cases. 

 Even in this compound fecundation there is no confusion of 

 types, but the hybrids are exactly such as would have arisen 

 from a simple impregnation with the pollen of one allied species. 

 In the course of a long series of experiments, seeds have occurred 

 very rarely containing more than one embryo ; and as it is pos- 

 sible that a pollen tube from either kind of pollen might have 

 simultaneously entered the ovule, these seeds might have con- 

 tained two embryos of a different nature : such, however, was 

 never observed to be the case by Gartner.* Nor, indeed, have 

 two distinct varieties occurred under such circumstances. 



Our author's observations contradict altogether the notions 

 entertained by many, and amongst them by Mr. Herbert, of the 

 possibility of varieties and half-hybrids arising from the admix- 

 ture of different kinds of pollen. Gartner has seen none, save 

 typical hybrids, arise from the intermixture of pure species. 



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 fecunda- 

 tion. 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 rep- 

 tiles, it has clearly no injurious if not a beneficial influence. 



It is a general rule that the pollen of a species possessing a 

 greater elective affinity neutralises the influence of that of one 

 less closely allied in that respect, as also does that of the matrix 

 the fertility of the pollen of another species. There are, how- 

 ever, two exceptions to this law : — 



I. In fertile hybrids, where neither the pollen of the male nor 

 female parent is effective, fecundation is produced by the pollen 

 of some pure, nearly allied species : as in Nicotiana rustico- 

 paniculata, on which the pollen of neither N. rustica nor N. 

 paniculata has any effect, impregnation is readily produced by 

 N. Langsdorfii. 



* Mr. Thwaites has found a compound embryo in the genus Fuchsia. 

 Two forms were grafted together, one possessing the character of F.fulgens, 

 the other of F. coccinea. It is clear, however, from his account, that they 

 did not arise from a union of pure species. The seedlings were too varied 

 to allow of such a supposition. See Ann. of Nat. Hist., 2nd series, vol. i. 

 p. 163. 



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