500 THE UNIVERSE. 



serve their virgin purity because their faithful visitors 

 consecrate the whole course of their ephemeral existence 

 to them, and never wander to another species. The noc- 

 turnal plants are also haunted by useful parasites, which 

 only awake to animation during the darkness.^ 



Conrad Sprengel even thinks that if so many flowers 

 are stricken Avith sterility in our hot-houses, even when 

 parading a superfluity of means for becoming mothers, it 

 is because their indispensable insect has not been allowed 

 to bear them company. This is the case with the Vanilla. 

 Since it blossoms in our country, it might fructify if kept 

 duly supplied with heat by means of a hot-air apparatus, 

 and yet it remains quite barren. The same thing happens 

 with the orange-coloured corollas of the Eoyal Strelitzia." 



It is especially in the two great families, the Asclepi- 

 adacea?, and Orchidace8e,the strange flowers of which remind 

 one of the forms and brilliant colouring of insects, that 

 nature seems to call the latter to her aid. In these the 

 anthers, which are like little glutinous clubs, attach them- 

 selves to the flies when these come to drink the nectar, 

 and are by them transported from one flower to another 

 and deposited upon the stigmata. But for such visitors 

 these plants would die out without progeny.^ 



^ Dr. Hililebrand of Bonn concludes, from several interesting experiments on the 

 fertilization of Cori/dalis cava, that when the flowers of the plant are protected 

 from insect influence and acted on onlyby theirown pollen thevproduce no capsules. 

 ^ The Kev. Conrad Sprengel, who assigned such a marvellous part in the 

 fecundation of plants to insects, in the excess of his enthusiasm called them 

 Nature's gardeners. The proof that the sterility of the Aromatic Vanilla ( Vanilla 

 aromatica, Limi.) in our greeuhouses is owing to the imperfect nature of the 

 fecundation, has been given by the experiments of M. Morren, who showed that by 

 placing the pollen itself upon the stigmata of the flowers fecundation was artificiall v 

 produced, and that plants were thus soon obtained which for beauty and aroma 

 might rival those produced by America. On the other hand, M. Brongniart arti- 

 ficially fecundated the Strelitzia regina, which, left to itself, is with us unproductive. 

 •^ Sometimes bees, when rifling the flowers of the Asclepiadacese or Orchises, 



