DISTRIBUTION OF SEXES. 



299 



The twelfth group comprises those species which bear pseudo-hermaphrodite 

 female flowers on one plant and pseudo-hermaphrodite male flowers on another. 

 This is observed in species of Buckthorn of the section Curvispina {Rhamnus 

 catliartica, saxatUis, tinctoria), in various Caryophyllaceee (e.g. Lychnis diurna 

 and vespertina), in Asparagus {Asparagus officinalis), the Rose-root {Rhodiola 

 rosea), the Mountain Currant (Ribes alpinum), and the Fuller's Thistle {Girsium). 



Fig. 287— Type of a dioecious plant: Crack Willow (Salix fragilis). 

 1 Twig with pistillate catkins. 2 Twig with staminate catkins. Natural size. 



The Mountain Cudweed (Gnaphalium dioiciira) and the closely allied species of 

 the same genus, Gnaphalium alpinum and carpaticum, also belong to this 

 group. 



The thirteenth group contains numerous species all bearing true pistillate 

 flowers on one plant and true staminate flowers on another; they were termed 

 dioecious by Linnaeus. Examples are : Ephedra, Cycads, Juniper, Yew, and Ginkgo 

 {Juniperus, Taxus, Ginkgo), numerous Sedges (e.g. Garex Davalliana, dioica), 

 Vallisneria (see flg. 155, vol. i. p. 667), Hemp and Hop {Gannahis, Humulus), 

 the Paper Mulberry {Broussonetia papyrifera: see flg. 229, p. 137), Dog's Mercury 



