776 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



upper are transformed into ribs and form a framework to which the valves are 

 applied. The two superior carpels are separated by a thin membrane, and bear the 

 ovules in two rows (see p. 75). The androecium is composed of two short and four 

 long stamens (see p. 292, fig. 284^). The pollen is adhesive. The fruit is a siliqua 

 (see p. 75 and p. 431, fig. 325 ^^' ^^). The seeds have no endosperm. The embryo 

 is curved. The cotyledons and also the foliage-leaves and 

 roots of most Cruciferse contain pungent and oily substances, 

 particularly Oil of Mustard, as is well known in the cases 

 of the Mustard-plant, Water-cress, Garden- cress, Radish, and 

 Horse-radish. 



The Cruciferse are distributed over the Northern Hemi- 

 sphere. They occur in greatest variety in the steppe-dis- 

 tricts of the Old World. The Mediterranean, Arctic, and 

 Alpine floras also include large numbers of these plants. 

 Amongst those Phanerogams which survive at the very 

 confines of vegetation in the Arctic regions, and on moun- 

 tains, are to be reckoned several Cruciferse. No fossil 

 remains are known. 



The Sarraceniacese are marsh- and water-plants, and 

 their leaves are adapted to the capture of insects (see vol. i. 

 p. 143 et seq.), whilst the rest of the Parietales grow chiefly 

 on rocky or sandy ground. The Parietales are distributed 

 over the warm and temperate parts of the Old and the New 

 World; the Cistacese belong especially to the flora of the 

 Mediterranean. The only known instance of fossil remains 

 is the fruit of a Poppy which was found in a deposit of 

 the Tertiary Period. The number of extant species hitherto 

 identified is about 3000. 



Fig. 437. — Parietales. 



1 Bixa Orellana (Bixaceae). Lon- 

 gitudinal section through a 

 flower-bud which i3 about to 

 open. ^ Argemone Mexicana 

 (Papaveracese). Longitudinal 

 section through the ovaiy. 

 (Magnified.) 



Alliance LV. — Malvales. 

 Families: Malvaceae, Sterculiacece, TiliacecB. 



Flowers actinomorphic, parts in whorls of 5. Sepals 

 free or connate, often valvate in bud. Stamens various, 

 often united. Carpels 3 to indefinite, united. Placentation 

 axile; seeds with endosperm. The Malvacese often possess an epi-calyx; fruit 

 usually splitting into 1-seeded mericarps. They include the Mallows (Malva), 

 Cotton-plants (Gossypium), Hollyhock (Althcea), &c. The Tiliacese are represented 

 by the Linden (Tilia), and the Sterculiacese include Theobroma Cacao, from which 

 chocolate is derived. 



There are nearly 200 species in this alliance. 



