600 APPENDIX. 



Apart from the true or confirmed monoecious plants, there are large num- 

 bers of hermaphrodite species known to exist, which are to all intents 

 and purposes practically monoecious, for either the pollen is shed before 

 the stigma is receptive (as in Agave, Lobeliads, Composites, &c.), or 

 the stigma develops itself and becomes fertilised by the pollen of older 

 flowers (as in Calceolaria) before its attendant anthers are fully developed 

 or part with their pollen. Again, many Orchids, Yuccas, and Ascle- 

 piads, are nearly entirely dependent on insect agency for their perfect 

 fertilisation, and thus they are peculiarly liable to cross-fertilisation or even 

 natural hybridism. The greater or less sexual affinity or consanguinity 

 of species, is proved by the more or less perfect manner in which hybrid- 

 ism can be made to take place' between them, as shown by the relative 

 quantity and quality of fertile seeds produced ; but of this relationship we 

 have no external evidence before hybridisation has been effected, since 

 species which closely resemble each other in every way cannot be made to 

 unite, while the reverse is frequently the result where great disparity in 

 size, habit, or colour would lead one to think otherwise. Again, two 

 species (or even two forms of a species) in a genus (A and B) may refuse 

 to hybridise i.e. , they will not interbreed ; but by crossing one of these 

 (say B) with a third species (C), the hybrids thus obtained will not unfre- 

 quently breed with A, as has been proved in the case of some kinds of 

 Nicotiana and Dianthus. This fact of some species refusing to interbreed 

 or unite sexually, except by the intervention of a third species, becomes all 

 the more singular and interesting when we remember the partial analogy 

 which exists when grafting is substituted for hybridising. Thus it is a 

 well-known fact that some varieties of Pear will not unite readily with the 

 Quince or Hawthorn stocks, and this difficulty is surmounted by the use 

 of "intermediate" stocks. Thus the Quince is grafted with the scion of a 

 Pear which is known to unite readily and succeed well on it as a stock, 

 and on this is worked the variety of Pear which refuses to unite well with 

 the Quince. 



M. Karl Koch, in a recent lecture on fruit-trees, says he has heard in 

 the East that some of our races of dessert Pears have descended from a 

 hybrid or hybrids obtained between the Pear and the Quince both of 

 which fruits are much more variable than is generally supposed from the 

 latter of which they have obtained flavour and aroma. Some kind of Pears 

 now grown closely resemble the Quince in shape, colour, and peculiarly 

 long calyx-lobes, as -well as in aroma and flavour ; and that such hybridity 

 is not improbable may to a certain extent be assumed, seeing that some 

 races of Pear show a marked preference for the Quince stock, while others 

 succeed only on the free stock or Pear. When writing the suggestions on 

 hybridising the Quince (see p. 471), I held the idea that hybridity had 

 occurred between that fruit and the Pear ; and I have no doubt but that 

 the possibility of this may be proved by any one who will undertake to 

 make experiments in crossing some of the European or Asiatic forms of 

 the Quince and Pear. 



Another fact of some importance connected with hybridisation is, that 

 part of the ovules in the same pod or capsule may become fecundated by 

 the pollen of one species, and part by another ; and when two species or 

 varieties are cross-fertilised, the elective affinity the competitive strength 

 or fixity of character possessed by each parent varies considerably, although, 

 as a general rule, the influence of the male or pollen parent is prepotent ; 

 nevertheless, that this is not always the case is proved by Mr Parkman's 

 and other hybridisers' experience with Lilies, and by the invariable pre- 

 potence of Gesnera zebrina and Nepenthes RafHesiana when cross-fertil- 

 ised reciprocally with other species of their respective genera. We find 



