PECULIARITIES OF HYBRIDS. 783 



in addition, which distinguish it from both of its parent-forms. One new property of 

 the hybrid, particularly of the variety-hybrid, for example, is the tendency to vary more 

 than the parent-form does : species-hybrids are usually sexually enfeebled, but those 

 of closely allied species are often more vigorous in their growth than the two parent- 

 forms, whereas the hybrids of more remote species are more feebly developed. The 

 luxuriant growth of hybrids between closely-allied species expresses itself in the de- 

 velopment of more numerous and larger leaves, higher and stronger stems, richer 

 root-systems, and more numerous shoots (stolons, layers), &c. Hybrids also have a 

 tendency to greater longevity, perennial hybrids arising from annual and biennial 

 parent-forms, but this is probably in consequence of the usually scanty seed-formation. 

 Moreover hybrids are noted for commencing to flower sooner, and for doing this 

 longer and more copiously than the parent-forms ; they sometimes produce extra- 

 ordinarily large numbers of flowers, which are moreover larger, better scented, more 

 intense in colour, and more persistent. The flowers of hybrids have a tendency to 

 become double, multiplying their carpellary and staminal leaves and developing them 

 as petals. In addition to this luxuriant growth the sexuality is mostly enfeebled, and 

 this in the most various stages. 'The stamens are in some cases completely developed 

 to all appearance, but are wholly or partly barren, since the pollen-grains do not attain 

 the normal perfection ; in other cases all the stamens are aborted and reduced to 

 minute rudiments. The pistil (carpels, ovaries) of hybrids cannot as a rule be 

 distinguished from those of the ancestral species, but their ovules are either incapable 

 of conception, or are only slightly capable of it ; no oospheres are formed, or the 

 embryo which begins to be developed from the oosphere perishes sooner or later. 

 In the most favourable cases, when seeds capable of germination are developed, they 

 exist in smaller quantities, and evince in their slow germination and in the short 

 period during which they maintain the power of germinating, a certain feebleness ' 

 (Naegeli). The enfeeblement of the sexuality is in some variety-hybrids hardly 

 noticeable, in others slight ; it increases as a rule in proportion with the remoteness of 

 the systematic relationship and sexual aflSnity of the ancestors. If the species-hybrids 

 are able to form seeds by self-pollination, the fertility usually decreases, on continued 

 self-pollination, from generation to generation, a phenomenon which perhaps depends 

 less on the sexual feebleness of the hybrids than on the circumstance that probably 

 the flowers of the hybrids have often been self-fertilised instead of being crossed 

 with other flowers or with other individuals of the same hybrids. According to 

 Naegeli, the rule may in general be applied that the male organs of species- 

 hybrids are enfeebled to a greater extent than the female; nevertheless there are 

 exceptions. 



(9) ' Hybrids generally vary in the first generation the less, the more remote in 

 relationship the ancestral forms are from one another ; and thus species-hybrids less 

 than variety-hybrids, the former often being distinguished by great uniformity, the 

 latter by great variability. If the hybrids are self-fertilised the variability increases 

 in the second and following generations the more, the more completely it was 

 wanting in the first; and three different varieties appear the more certainly, the 

 more remote the parent-forms are from one another — one, which agrees with the 

 original type, and two others which more resemble the parent-forms. These varieties 

 have, however, at least in the earlier generatidns, litHe constancy, and are not trans- 



