274 NATURAL SCIENCE. 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 is. 6d. (it is now 

 quoted by Friedliinder 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 MuUer, 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. t r^ wt , r. 



^ John C. Willis. 



