228 REVIEWS. 



flowers to branches, scenting some with essential oils, and 

 leaving others unscented ; and the insects were attracted to 

 the former in an unmistakable manner." 



" Of all colors white is the prevailing one ; and of white 

 flowers a considerably larger proportion smell sweetly than of 

 any other color, namely, 14.6 per cent. ; of red, only 8.2 per 

 cent, are odoriferous. The fact of a larger proportion of white 

 flowers smelling sweetly may depend in part on those which are 

 fertilized by moths requiring the double aid of conspicuous- 

 ness in the dusk and of odor. So great is the economy of 

 nature, that most flowers which are fertilized by crepuscular 

 or nocturnal insects emit their odor chiefly or exclusively in 

 the evening. Some flowers, however, which are highly odor- 

 iferous depend solely on this quality for their fertilization, 

 such as the night flowering-stock (Hesperis) and some species 

 of Daphne ; and these present the rare case of flowers which 

 are fertilized by insects being obscurely colored." 



" The shape of the nectary and of the adjoining parts are 

 likewise related to the particular kinds of insects which habit- 

 ually visit the flowers : this has been well shown by H. Miiller, 

 by his comparison of lowland species, which are chiefly visited 

 by bees, with alpine species belonging to the same genera, 

 which are visited by butterflies." 



"Pollen contains much nitrogen and phosphorus, — the two 

 most precious of all the elements for the growth of plants, — 

 but in the case of most open flowers, a large quantity of pollen 

 is consumed by pollen-devouring insects, and a large quantity 

 is destroyed during long-continued rain. With many plants 

 this latter evil is guarded against, as far as possible, by the 

 anthers opening only during dry weather, by the position and 

 form of some or all of the petals, by the presence of hairs, 

 etc. ; also, as Kerner has shown in his interesting essay, by 

 the movements of the petals or of the whole flower during 

 cold and wet weather. In order to compensate the loss of 

 pollen in so many ways, the anthers produce a far larger 

 amount than is necessary for the fertilization of the same 

 flower. I know this from my own experiments on Ipomsea, 

 given in the Introduction ; and it is still more plainly shown 



