Chap. XXIV. ARRESTED DEVELOPMENT AND RUDIMENTS. 307 



abortion travels downwards and outwards, and all the flowers 

 become rudimentary ; but the abortive stamens and pistils are not 

 so small in the lower as in the upper flowers. In the Viburnum 

 opulus, on the other hand, the outer flowers naturally have their 

 organs of fructification in a rudimentary state, and the corolla is of 

 large size; under cultivation, the change spreads to the centre, and 

 all the flowers become affected. In the compositaa, the so-called 

 doubling of the flowers consists in the greater development of the 

 corolla of the central florets, generally accompanied with some degree 

 of sterility ; and it has been observed 8G that the progressive doubling 

 invariably spreads from the circumference to the centre, — that is, 

 from the ray florets, which so often include rudimentary organs, to 

 those of the disc. I may add, as bearing on this subject, that with 

 Asters, seeds taken from the florets of the circumference have been 

 found to yield the greatest number of double flowers. 87 In the 

 above cases we have a natural tendency in certain parts to be rudi- 

 mentary, and this under culture spreads either to, or from, the axis 

 of the plant. It deserves notice, as showing how the same laws 

 govern the changes which natm'al species and artificial varieties 

 undergo, that in the species of Carthamus, one of the Composita?, a 

 tendency to the abortion of the pappus may be traced extending 

 from the circumference to the centre of the disc as in the so-called 

 doubling of the flowers in the members of the same family. Thus, 

 according to A. de Jussieu, 88 the abortion is only partial in Cartha- 

 mus creticas, but more extended in ft lanatus ; for in this species 

 only two or three of the central seeds are furnished with a pappus, 

 the surrounding seeds being either quite naked or furnished with a 

 few hairs ; and lastly in ft tinctorius, even the central seeds are 

 destitute of pappus, and the abortion is complete. 



With animals and plants under domestication, when an organ 

 disappears, leaving only a rudiment, the loss has generally been 

 sudden, as with hornless and tailless breeds ; and such cases may be 

 ranked as inherited monstrosities. But in some few cases the loss 

 has been gradual, and has been effected partly by selection, a% 

 with the rudimentary combs and wattles of certain fowls. We 

 have also seen that the wings of some domesticated birds have been 

 slightly reduced by disuse, and the great reduction of the wings 

 in certain silk-moths, with mere rudiments left, has probably been 

 aided by disuse. 



With species in a state of nature, rudimentary organs are 

 extremely common. Such organs are generally variable, as 

 several naturalists have observed ; for, being useless, they are 

 not regulated by natural selection, and they are more or less 

 liable to reversion. The same rule certainly holds good with 



86 Mr. Beaton, in 'Journal of Hor- 1862, p. 233. 

 ticultuve,' May 21, 1861, p. 133. 88 ' Annales du Museum,' torn, vi 



47 Lecoq, ' De la Fecondation,' p. 319. 



X 2 



