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 Caryophyllaeeae (e.g. Lychnis div/rna 

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

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



Hg. 287.— Type of a dioecious plant: Crack Willow (Saliafragilis). 

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



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

 the same genus, Gnaphalium alpinv/m 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 

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

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

 ValMsneria (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 



