274. NATURAL SCIENGE. APRIL, 1893. 
honey from the rain ; (4) arrangements to enable insects easily to find 
the honey, such as size and colour of the corolla, scent, and the 
honey-guides or ‘‘path-finders” formed by the differently-coloured 
spots near the entrance to the honey; (5) the general impossibility of 
spontaneous self-fertilisation, owing largely to dichogamy or other 
arrangements, and the necessity of insect aid. 
The book contains an enormous mass of the most painstaking 
observations on numerous flowers, undertaken with these ideas in 
view. There is, however, one very serious blemish in it, which, 
perhaps, as much as anything, caused its rejection by botanists. 
Sprengel was most careful to find reasons for everything in the struc- 
ture of the flower, and yet he did not try to give a reason for flowers 
being adapted to fertilisation by insects. Why should a flower go to 
the trouble and expense of attracting insects merely to effect fertilisa- 
tion, which it might do for itself very easily? Sprengel observed 
that by dichogamy and other arrangements it constantly occurred 
that a flower was fertilised, not with its own pollen, but with pollen 
from a different flower. He even went so far as to say, ‘‘ Since very 
many flowers are unisexual, and apparently at least as many of the 
hermaphrodites are dichogamous, Nature seems to have intended 
that no flower should be fertilised by its own pollen,” and yet he did 
not suspect that this was the whole point of the fertilisation by insect 
agency. Darwin and others have shown the great benefits arising 
from cross fertilisation, and have thus explained why plants should 
have become adapted to fertilisation by insects in the various ways 
described by Sprengel. Had Sprengel been aware of this point, and 
incorporated it in his theory of flowers, it seems unlikely that his 
work could have fallen into the oblivion which soon overtook it. 
Even so late as 1850, the work could be bought for 1s. 6d. (it is now 
quoted by Friedlander at 22s.). In 1841 it came into the hands of 
Charles Darwin. ‘‘ The book impressed him as being ‘ full of truth,’ 
although with ‘ some little nonsense.’ It not only encouraged him in 
kindred speculation, but guided him in his work, for in 1844 he speaks 
of verifying Sprengel’s observations ” (Life, by Francis Darwin). He 
rehabilitated Sprengel by his biological work, especially the ‘ Origin 
of Species,” the ‘‘ Cross and Self-Fertilisation of Plants,” where he 
recounted the results of a long series of experiments showing the bene- 
fits of cross fertilisation, and, lastly, by his brilliant work on ‘“ Fertili- 
sation of Orchids,” a book of observations on flowers, conducted much 
on Sprengel’s lines, but with the flaws of his theory removed. Since 
this time, the whole subject of fertilisation, by insects and otherwise, 
has received much attention at the hands especially of Hildebrand, 
Axell, Delpino, Hermann and Fritz Miller, and recently Macleod and 
Robertson. To the writings of these authors, reference must be made 
for further information, and we must here take our leave also of 
Sprengel, a man deserving of a high place in the History of Botany, 
but most unjustly forgotten for nearly seventy years after the 
publication of his classic book. Joun C. Wits. 
