PTERIDOPHYTA 545 



Psorospermum Spach. Guttiferae (11). 20 trop. Afr. , Madag. 



Psychine Desf. Cruciferae (2). i N. Afr. 



Psychotria L. (excl. Mapourea Aubl.). Ruhiaceae (n. 5). 400 trop. 

 Some heterostyled. Many have infl.-axis brightly coloured. [For 

 P. Ipecacuanha Stokes see Uragoga.] 



Psychrobatia Greene (Rubus p.p.). Rosaceae (in. 2). i N.W. Am. 



Psychrogeton Boiss. (Aster -p.p. BH.}. Compositae (3). i Afghanistan. 



Psychrophyton Beauverd (Raoulia p.p.). Compositae (4). 9 N.Z. 



Psyllium Tourn. ex Juss.= Plantago L. p.p. (Plantag. ). 



Psyllocarpus Mart. Rubiaceae (n. 10). 5 Brazil. 



Psyllothamnus Oliv. Caryophyllaceae (i. 4). i Aden. 



Ptaeroxylon Eckl. et Zeyh. Meliaceae (i) (Sapind. BH.}. \ S. Afr., 

 P. ittilc: E. et Z. (sneeze wood, cape mahogany), timber. 



Ptarmica (Tourn.) Neck. = Achillea L. p.p (Comp.). 



Ptelea L. Rutaceae (iv). 60 N. Am. P. trifoliata L. cult. orn. shrub 

 (shrubby trefoil). Fls. monoec. Fr. winged (if. Ulmus). 



Pteleocarpa Oliv. Boragin. (n) (Olacin. BH.}. 2 Malay Pen., Borneo. 



Ptelidium Thou. Celastraceae. i Madag. 



Pteleopsis Engl. Comhretaceae. 4 E. trop. Afr. 



Pteralyxia K. Sclium. ( Vallesia p.p.)- Apocyn. (i. 3). i Hawaiian Is. 



Pterandra A. Juss. Malpighiaceae (n). i Brazil. 



Pteranthus Forsk. Caryophyllaceae (i. 6). r Medit. 



Pterichis Lindl. Orchidaceae (n. 2). 6 trop. S. Am. 



Pteridium Gled. i cosmop., P aquiliniini Kuhn, the bracken. It has 

 a creeping rhiz. , bearing 2 ranks of 1. At the base of the 1. is a nectary, 

 which ants visit. The sori are confluent along the 1. margin, which is 

 curved over them, while there is also a true indusium on the inner side 

 of the sori (the char, of distinction from Pteris, in which the bracken 

 used to be placed). Adv. buds appear on the back of the 1. stalk, 

 near the base. 



Pteridocalyx Wernham. Rubiaceae (i. 3). i Brit. Guiana. 



Pteridophyllum Sieb. et Zucc. Papaveraceae (i). i Japan. 



Pteridophyta Vasailnr Cryptogams, one of the four chief divisions 

 of the Vegetable Kingdom. They have a well marked alternation of 

 generations, the gametophyte (oophyte or sexual generation) being 

 insignificant in size compared to the sporophyte (asexual generation), 

 but still capable of independent growth. The life history of a typical 

 Pteridophyte may be shown diagrammatically as follows, taking the 

 fern as an example : 



Fern-plant -* sporophylls -* sporangia -> spores 



t f 



I spermatozoid *- antheridia ) 



fertilised ovum *- { .}*- prothallus. 



| ovum -*- archegonia | 



The 'plant' or asexual generation alternates with the prothallus or 

 sexual generation. In many P. there are 3 and 9 prothalli. The pro- 

 thallus corresponds to the 'plant' in a moss or liverwort, whilst the 

 sporogonium of these latter = 'plant' in a fern or lycopod. 



The plant itself takes various forms in the different groups. Except 

 in tree ferns and in fossil forms it does not attain great size. There 

 is an erect stem in many ferns, &c. ; others have creeping stems 

 (e.g. Lycopodium and Selaginella), rhiz. (many Ferns), or floating 



w. 35 



