1826 



A TEXTBOOK OF THEORETICAL BOTANY 



tissue surrounding the vascular bundles. In other types mucilage 

 cells are scattered through the mesophyll. Other features of anatomical 

 interest are the production of cork from the epidermis and the presence of 

 resinous material stored up in the heart wood. 



One species of economic importance is Guaiaciim officinale (Fig. 1728) 

 (Lignum Vitae), a small tree which is found growing in the dry coast areas 

 of the West Indies and Central America. The greenish-brown heart wood 

 yields a bitter resin which is used medicinally and also as a test reagent. 

 Tribuhis terrestris develops spiny, schizocarpic fruits which are readily 

 carried about by animals. It is found in dry sandy districts of southern 

 Europe, central Asia and tropical Africa. Porliera hygrometrica shows 

 an interesting physiological behaviour. The leaflets spread out hori- 

 zontally by night, but by day they fold up in pairs and thus avoid excessive 

 transpiration. It is a native of Mexico and the Andean region of South 

 America. Larrea mexicana is the so-called Tar Bush or Creosote Plant, 

 which forms a dense scrub vegetation and serves to bind loose sand 

 together. It has an offensive smell which prevents animals from eating it. 

 The seeds of Peganum harniala yield a dye known as Turkey Red. 



Geraniaceae 



The family is a small one but is fairly well represented in the British 

 Flora. The best-known genera are Geranium (Crane's-bill) and Eiodium 

 (Stork's-bill); both are represented in Britain by a number of species, of 

 which we may mention Herb Robert (G. robertianum), Meadow Crane's- 

 bill [G. pratense) and Mountain Crane's-bill (G. sylvaticum). 



It should be noted that the so- 

 called Geraniums so extensively 

 grown in gardens and greenhouses 

 belong to the genus Pelargonium, 

 which is South African. 



The plants are mostly annual 

 or perennial herbs with swollen, 

 jointed nodes often covered with 

 glandular hairs. The leaves may be 

 either alternate or opposite. They 

 may be palmate but many are 

 palmatisect and most are stipulate. 

 The flowers (Fig. 1729) may 

 „ T7, , , c r^ ■ be solitary or may be borne in 



Fig. 1720- — rloral diagram oi Lreraniiini -^ -' 



pratense. Geraniaceae. (After Eicliler.) cymose infioreSCCnceS, generally 



composed of a small number of flowers. They are usually actinomorphic, 

 pentamerous and hypogynous. 



The calyx is polysepalous and consists of five persistent sepals which 

 are well developed and green in colour. They are imbricated in the 

 bud. 



