
TROPHOLUM PEREGRINUM AND T. SPECIOSUM. 231 
by natural selection ina form more or less resembling 7. peregrinum. Lastly, that 
circumstances might cause successively earlier penetrations to become fixed, until 
a form might be reached such as we have in 7. speciosum, where the extra-seminal 
root penetrates the carpel as soon as it makes its exit through the seed-coats. 
Such speculations are no doubt very attractive, but, in my opinion, are 
much to be deprecated. The Darwinian hypothesis is so essentially of the 
nature of a speculation which, at the best, can only have a balance of proba- 
bilities in its favour, that it must always be eminently hazardous to build, by 
speculation upon speculation, a structure which is liable at any time to fall to 
pieces from want of inductive foundation on fact. 
With regard to the present case, the following objections occur to me as 
applicable to the supposed ‘“ descent-by-modification ” of 7. speciosum, which I 
have indicated above :— ; 
1st, It seems highly improbable that such a variation as I have shown in 
T. majus, even although a favourable one, should ever have become of vital 
importance. It is far too slight to render it in the least probable that any 
change of conditions should have ever arisen to render its non-possession fatal. 
2d, The impediments to self-fertilisation and the provisions for cross- 
fertilisation (dichogamy, conspicuous colour and shape of flowers, secretion of 
nectar, &c.) in these plants, would render extremely probable, if not almost 
certain, the obliteration of any such variation almost as soon as it appeared ; * 
and thus the chances of a concurrence of such variation and the change of con- 
ditions necessary to make it of vital importance would be almost infinitely small. 
It has been suggested to me by a critical friend, that the penetration of the 
carpel may possibly not have the importance attributed to it in the case as above 
given, and that the penetration may be merely a developmentally correlated 
adjunct to some more important modification which has been the immediate 
subject of natural selection. It appears to me, however, that the suggestion of 
such a possibility does not materially affect the question. If diverse species, 
either of plants or animals, have been produced by the fixture of modifications 
by natural selection—whether in the struggle with adverse conditions of life, in 
sexual competition, or otherwise—it may safely be assumed that the successive 
modifications so selected would always have been slight, inasmuch as any abrupt 
or violent divergence from the type almost necessarily partakes of the nature of 
a monstrosity, involving inherent weakness, and thus absence of the elements 
of permanence. My argument, therefore, may be regarded as capable of general 
application, whether it is the carpellary penetration or an unknown something, 
which may be supposed to have been the immediate subject of natural selection. 
* As I have elsewhere stated, in a semi-popular lecture on “‘ Consanguineous Marriages” (Glasgow 
Med. Journal, Feb. 1872), the use or function of sexual reproduction, as distinguished from gemmation, 
seems to be this very obliteration of individual variations, so as “ to keep up an average tone or quality 
in the species, and, by dilution of individual peculiarities, to eliminate possible sources of evil on their 
appearance.” 
VOL. XXVII. PART II. 3.0 
