THE DICOTYLEDONES 1741 



stem. The flowers are borne early in the spring in the axils of last year's 

 leaves (Fig. 161 8). They are monoecious, though frequently both kinds of 

 flowers occur in the same inflorescence, the central ones being female and 

 the lateral flowers, which develop later, being male, a point which dis- 

 tinguishes this genus from most of the others in the family. These flowers 

 contain no nectar and are wind-pollinated. Each flower (Fig. 1619) consists 

 of from five to seven polysepalous segments, inside which, and opposite 



Fig. 1619. — Ulrmis moutann. Single flower. 



to them, are a similar number of stamens. The ovary is made up of two 

 carpels forming a single chamber, or occasionally two chambers. It contains 

 a single anatropous ovule. 



The British species of UJmiis deserve a short note. In the first place 

 there are a number of common but quite distinct species of which we may 

 cite the following : 



1. U. procera {U. campestris). English Elm. This is the largest and 



commonest species in southern England, which may be found 

 either in rows, in hedges, or separately in parks. It is a hybrid 

 and does not produce fertile seeds but propagates readily by 

 suckers. In spite of its name it is not a native British species, 

 but was traditionally introduced by the Romans. It does not 

 occur spontaneously, but is widely planted for its timber and its 

 stately form. 



2. U. sativa. Small-leaved Elm. This species diflFers from U. procera 



only in the size of the leaves, which are smaller. It may in fact 

 be only a variety. It occurs chiefly in the eastern counties. 



3. U. carpinifoUa (U. nitens). Smooth-leaved Elm. It is usually 



distinguished by the texture of the leaf which is smooth, and the 

 veins not so clearly marked. It may be a variety of V. glabra 

 and is restricted to the eastern counties. 



4. U. glabra (including U. mojitana). The Wych Elm. It is a large 



tree with more or less arched branches. The leaves are sessile, 

 acuminate, smooth and shiny on the upper surface, but with 

 hairs in the vein-axils beneath. It frequently forms suckers and 



