DISTRIBUTION OF SEXES. 



299 



Tlie twelfth group comprises those species which bear pseudo-herrnaphroilite 

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

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

 cathartica, saxatilis, tinctoria), in various Caryophyllacese (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 (Cirsium). 



Fig. 287. — Type of a dioecious plant: Crack Willow {Salix fragilU). 

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



The Mountain Cudweed {Gnaphalium dioicum) and the closely allied species of 

 the same genus, Gnaphaliwin 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 Linn^us. Examples are: Ephedra, Cycads, Juniper, Yew, and Ginkgo 

 (Juniperus, Taxus, Ginkgo), numerous Sedges (e.g. Carex 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 



