10 
POPULAR SCIENCE REVIEW. 
The preceding will be sufficient to prove that self-fertilisation 
is a great and wide-spread fact in the vegetable world ; and 
that, so far as the plants themselves are concerned, they show 
no features which imply degeneracy of any kind. They are very 
abundant. Nearly all of our “ most troublesome weeds ” are 
habitually self-fertilising, and show no signs of extinction what- 
ever. Their power of propagation is simply enormous. 
Now arises the question as to what is the right interpretation 
of this fact. My idea is, that self-fertilisation is the legitimate 
or primeval condition of plants ; that for the sole end of plant- 
life — propagation — extraneous aid is quite superfluous ; and that 
plants have become adapted to insects, is, so to say, an acci- 
dental circumstance of no value at all, so far as the securing of 
a sufficient supply of seed is concerned ; that the notion that 
plants must be crossed to be kept up is a wrong surmise, which 
is not really at all borne out even by Mr. Darwin’s experiments. 
Let us briefly review those results. One plant alone was 
cultivated for several years, Ipomcea purpurea , or the so-called 
Convolvulus major . On turning to page 53 of his work on 
“ Cross and Self-fertilisation of Plants,” the respective heights 
of the crossed and self-fertilised individuals will be seen exhi- 
bited in a tabular form. There is no steady increase in favour 
of the intercrossed, but a series of maxima and minima . On 
the other hand, there is a steady decline in the heights of the 
crossed when a series of averages are taken for every successive 
three years, a fact which Mr. Darwin does not seem to have 
observed. Although the actual heights of the intercrossed 
plants were in every year greater than those of the self-fertilised, 
yet the ratios taken as above proposed are as follows : For the 
first three years as 100: 74*3; for the second three years as 
100 : 7 7 # 6 ; and for the third three as 100 : 81*6. The inter- 
pretation of this can only be that while 66 crossing ” imparted a 
stimulus to vegetative vigour, it is not permanent , but at the 
above rate of decrease the crossed plants would have become 
lowered in height, and be equal to the self-fertilised in a few 
more generations.* 
With Mimulus luteus a strong self-fertilising form arose 
under Mr. Darwin’s cultivation, so that it was quite useless to 
continue the experiment after seven generations, as the self- 
fertilised form entirely surpassed the intercrossed. 
As it was with the heights so was it with fertility. The 
advantages gained at first were not apparent after a few genera- 
tions, and the self-fertilised, then, beat their opponents, f 
* 100 is the assumed standard for the intercrossed ; the ratios, therefore, 
appear to show a steady improvement in the self-fertilized. 
t For arguments and statistics I must again refer the reader to my 
original paper (/.<?.). 
