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 

 cathartica, saxatilis, tinctoria), in various Caryophyllacese (e.g. Lychnis cliurna 

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

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



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

 1 Twig with pistillate catkins. 2 Xwig with stamlnate catkins. Natural size. 



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

 the same genus, Onaphaliurti 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 fig. 155, vol. i. p. 667), Hemp and Hop (Cannabis, Humulus), 

 the Paper Mulberry (Broussonetia papyrifera; see fig. 229, p. 137), Dog's Mercury 



