72 THE POPULAR SCIENCE MONTHLY. 



had long been known that the cowslip and primrose exist under two 

 forms, about equally numerous, and differing from one another in the 

 arrangements of their stamens and pistils ; the one form having the 

 stamens on the summit of the flower and the stigma half-way down, 

 while in the other the relative positions are reversed, the stigma being 

 at the summit of the tube and the stamens half-way down. This dif- 

 ference had, however, been regarded as a case of mere variability ; but 

 Darwin showed it to be a beautiful provision, the result of which is 

 that insects fertilize each flower with pollen brought from a different 

 plant ; and he proved that flowers fertilized with pollen from the other 

 form yield more seed than if fertilized with pollen of the same form, 

 even if taken from a different plant. 



Attention having been thus directed to the question, an astonish- 

 ing variety of most beautiful contrivances has been observed and 

 described by many botanists, especially Hooker, Axel, Delpino, Hilde- 

 brand, Bennett, Fritz Miiller, and, above all, Hermann Miiller and 

 Darwin himself. The general result is that to insects, and especially 

 to bees, we owe the beauty of our gardens, the sweetness of our fields. 

 To their beneficent though unconscious action flowers owe their scent 

 and color, their honey nay, in many cases, even their form. Their 

 present shape and varied arrangements, their brilliant colors, their 

 honey, and their sweet scent are all due to the selection exercised by 

 insects. In these cases the relation between plants and insects is one 

 of mutual advantage. In many species, however, plants present us 

 with complex arrangements adapted to protect them from insects ; 

 such, for instance, are in many cases the resinous glands which render 

 leaves unpalatable ; the thickets of hairs and other precautions which 

 prevent flowers from being robbed of their honey by ants. Again, 

 more than a century ago our countryman, Ellis, described an Ameri- 

 can plant, Dioncea, in which the leaves are somewhat concave, with 

 long lateral spines and a joint in the middle ; close up with a jerk like 

 a rat-trap the moment any unwary insect alights on them. The plant, 

 in fact, actually captures and devours insects. This observation also 

 remained as an isolated fact until within the last few years, when 

 Darwin, Hooker, and others have shown that many other species have 

 curious and very varied contrivances for supplying themselves, with 

 animal food. 



Some of the most fascinating branches of botany morphology, 

 histology, and physiology scarcely existed before 1830. In the two 

 former branches the discoveries of Von Mold are preeminent. He first 

 observed cell-division in 1835, and detected the presence of starch in 

 chlorophyl-corpuscles in 1837, while he first described protoplasm, 

 now so familiar to us, at least by name, in 1846. In the same year 

 Amici discovered the existence of the embryonic vesicle in the embryo 

 sac, which develops into the embryo when fertilized by the entrance 

 of the pollen-tube into the micropyle. The existence of sexual repro- 



