550 PHYSIOLOGY. 



therefore return, further explaining this reciprocal relation in indi- 

 vidual instances. 



Very many, indeed we may say the majority of plants are furnished 

 with nectaries which secrete a honey, which many insects, particularly 

 the Lepidoptera and bees, seek very greedily. To procure this honey, 

 those insects fly, some by day in the sunshine, and others in the twilight 

 from flower to flower, visit each, and here for a time imbibe the freshly- 

 secreted juices. They cannot avoid sweeping off the farina that has 

 just escaped from the anthers with their rough hairy bodies, and which 

 they bring into contact with the stigma, for both organs must frequently 

 be pushed on one side by the insect visiting the flower before it can 

 reach the nectaries. Some observers have remarked that insects are 

 very particular in the selection of flowers, and at one flight visit but 

 the blossoms of one kind of plant. This, according to Ch. K. Sprengel, 

 occasions the impregnation of flowers, for in the majority of flowers the 

 anthers and stigma have not the same degree of ripeness, but either the 

 one or the other is the earliest. As insects visit only flowers of the same 

 species, they now meet with those that have ripe anthers and now with 

 those with ripe stigmata, and cause impregnation by bringing the ripe 

 pollen into contact with the ripe stigma. Also, as Kolreuter has 

 already remarked, and later observations have tended to confirm, the 

 majority of flowers cannot be impregnated by their own pollen, but 

 require that of other individuals, just as the hermaphrodite Mollusca 

 require a mutual connexion, and cannot impregnate themselves ; and if 

 this law be general, which, however, does not appear to be the case, 

 insects alone can be the means by which nature attains the full object 

 of plants, namely, their impregnation and formation of seed. 



If in many cases by other means, namely, by wind and rain, both of 

 which shake the flowers, and thus bring the pollen into contact with the 

 stigma, impregnation is effected, yet in very many it appears to be 

 possible only through the assistance of insects. This is the case in 

 dioecious plants, namely, in the sallows and poplars, which blossom 

 early in the year. In these also the male flowers are the earliest, the 

 female ones the latest ; both contain nectaries, and are therefore much 

 visited by bees and flies. It is only thus that the female flowers can 

 be impregnated by means of the pollen hanging to the insect. This is 

 the case also with the dioecious palms, namely, in Phcenis dactyhfera, 

 the male of which is the rarest in its country, and is frequently at 

 many miles distance from the female. Also many monoecious plants, 



