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POPULAR SCIENCE REVIEW. 
highly attractive to insects, and, as has been shown by Sprengel 
in 1790, and by various botanists at the present day, are specially 
adapted to insects who transfer the pollen from one flower to 
another. 
The effects of the last-mentioned process have been ascer- 
tained and described by Mr. Darwin in his work on “ Cross and 
Self-Fertilisation of Plants.” He proved, by experiments, that 
when ordinary garden plants are crossed by others of the same 
stock, or by others of a different stock of the same species, the 
offspring generally showed greater vegetative vigour in growing 
taller and in bearing more vigorous and greener foliage ; while 
in their reproductive organs there was brighter and greater 
variation in colour, and often more seed was set than when such 
plants had been continuously self-fertilised. 
The results would seem, therefore, to exactly fulfil an infer- 
ence which the late Dean Herbert drew from his experiments 
with bulbous plants, and which he has recorded in his work on 
the Amaryllidece (p. 70), as follows: — “ I am inclined to think 
I have derived advantage from impregnating the flowers from 
which I wish to obtain seeds, from individuals of another variety 
or another flower, rather than its own, and especially of any 
grown in different soil or aspect.” 
A very considerable amount of literature now exists on the 
subject of cross fertilisation by insect agency. The beautiful 
and exquisite adaptations exhibited by so many conspicuous 
flowers have attracted the attention of observers, so that whoever 
sets to work to examine flowers with this object in view, is pretty 
sure of making new discoveries of special adaptations. 
So obvious, then, has the importance of insect agency been 
thought to be, that the inference has been drawn that cross fer- 
tilisation is necessary for flowers ; and Mr. Darwin generalised 
this inference into an aphorism, which may be regarded as ex- 
pressing the exactly opposite view to that attributed to Linnaeus, 
namely, that “ Nature abhors perpetual self-fertilisation.” We 
may contrast these opposite poles of thought, somewhat as fol- 
lows: — With Linnaeus, Nature had specially designed (most?) 
flowers to secure self-fertilisation. With Darwin, Nature has 
specially adapted (most?) flowers to avoid self-fertilisation. 
I add “ most ?” because these observers do not fail to see 
that there are exceptions in both cases. 
Opinions have often been compared to a pendulum, whether 
they be political, ecclesiastical, or otherwise, in that for a time 
they run high in one direction ; but a reaction sets in and down 
they go, and are then carried up to the opposite extreme. It is 
not till both extreme forms have been well tested that at last 
the excesses in both are struck off, and the truth which invariably 
underlies each is at last recognised, and the u golden mean ” is 
