THE HOYA AND STEPHANOTIS FAMILY. 195 



savica and A. tuberosa being common examples. Another 

 distinct group is the succulent - stemmed leafless "Carrion- 

 flowers," or Stapeliads, the twining Stephanotis, the honey- 

 distilling Hoyas, the shrubby Centrostemma, and the curious 

 hooded or dome-flowered Ceropegias. Their fertilisation* de- 

 pends to a great extent on insect agency, and Professor 

 Riley has recommended horticulturists who are much troubled 

 with bees to plant Asclepias cornuta (Silk-weed), of the nectar 

 from which bees are passionately fond ; and in their visits 

 to the flowers of this plant they become so laden with the 

 viscid pollen - masses that they fall down and die in great 

 numbers. From the 'Treasury of Botany/ p. 99, we learn 

 that "the manner in which the ovules of these plants 

 (Asclepiads) are fertilised by the pollen is among the most 

 curious phenomena known in plants. Instead of the grains 

 of pollen falling on a viscid stigmatic surface, and then pro- 

 -ducing tubes of impregnation, the tubes are formed inside 

 the pollen-bags, whence they ultimately find their way by a 

 spontaneous emission, and reach the surface of the stigma 

 without being projected upon it, conducted by some inherent 

 vital power." (See ' Lind. Med. Bot.,' 4th ed.) The tubular 

 flowers of Stephanotis, like those of some Dogbanes, and those 

 of Aristolochia clematitis, are set with rigid deflexed hairs 

 inside the tube, the use of these being to entrap any flies 

 which enter, and keep them prisoners until fertilisation has 

 been effected, after which they lose their stiffness, and allow 

 the insect to escape. Arauja (Physianthus) albens also entraps 

 the humming-bird hawk-moth by a singular movement of the 

 waxy pollen - masses. Asclepiads can be distinguished from 

 Apocynads (Dogbanes) only by their Orchid-like or waxy pollen. 

 The following are the principal cultivated genera : Asclepias, 

 Stephanotis, Centrostemma, Hoya, Ceropegia, Brachystelma, 

 Apteranthes, and Stapelia. 



Hoya (Honey or Wax Flowers). A genus of scandent 

 tropical Asclepiads, principally natives of Java, China, and 

 New Holland, and represented in our gardens by H. carnosa, 

 H. bella, H. Paxtoni, H. imperialis, and several others. There 

 is a creamy variegated form of H. carnosa. All the species 

 may be readily propagated either by stem or leaf cuttings, in 

 heat, and covered with a bell-glass. H. carnosa and H. 

 Paxtoni bear fruit rarely, a circumstance owing in all pro- 

 bability to their flowers being accidentally fertilised by insect 

 agency. Seeds grow freely sown in light sandy earth in a 



* See ' Trans. Linn. Soc.,' xvi. 685 and 715, for account of their sexual 

 organs and methods of fertilisation. 



