352 



DICOTYLEDONES. 



The flowers are situated in inflorescences which develop from 

 the lower buds of the shoot of the preceding year. The lowermost 

 bud-scales are empty, the uppermost support either solitary flowers, or small, 

 dichasial or unipared scorpioid inflorescences. The terminal bud on tbe vege- 

 tative shoot quickly falls off, and the 

 upper lateral bud continues the growth 

 sympodially. Flowering takes place 

 before the leaf-buds open. The flowers 

 are wind-pollinated and have no honey. 

 Fossil species have been found in the 

 Oligocene. 



20 species ; North Temp. (2 species 

 in this country). Important as timber. 

 The Cork-elm (U. sttberosa) has a rather 

 thick cork, which, however, is of no 

 technical use. The bast is used as 

 Lime-bast. 



B. CELTIDE.E. The fruit is a drupe, 

 the embryo curved, with folded or rolled 

 up cotyledons, with or without endo- 

 sperm. The anthers are introrse. The 

 flowers are borne on a shoot of the 

 same year. Planera (N. America) ; 

 Zelkora. About 114 species; especially 

 N. Temp., Trop. 



FIG. 339. A Ulmus campestris, flower 

 with exceptionally aborted g.ynoeceum; 

 B, U. effnaa, flower with 8 stamens ; C, U. 

 cuiiipe-ftn's, fruit opened in front to show 

 the seed pendulous from the apex of the 

 loculus ; one loculus is aborted. 



Order '2. Urticaceae 



(Nettles). The majority of spe- 

 cies are herbs with simple, stipu- 

 late leaves ; they have no latex ; 

 stinging liairs abundant. The flowers (Fig. 340) are unisexual, gene- 

 rally 2-meroQS and arranged in clusters, -which are united into 

 catkin-like inflorescences. The perianth is composed very often of 

 4 (2 + 2) free, or in the ? -flowers generally united, green leaves ; 

 the 4 (2 + 2) stamens are opposite the perianth-leaves, the filaments 

 are bent inwards in the bud and throw themselves elastically 

 towards the outside. The gynoeceuni has one style and one stigma 

 (capitate or brush-like, Fig. 341) ; the ovary is unilocular, with one 

 orihotropous, erect ovule (all other orders of this family have inverted 

 or curved ovules). Fruit, a nut or drupe. Endosperm present 

 (in Urtica very little), oily. Embryo straight. The STINGING HAIRS 

 are club-shaped, very turgid, and provided with a siliceous, brittle apex, 

 which breaks off in an oblique direction and allows the poisonous cell-sap to 

 be forced out. In many tropical Nettles this is so strong that it may produce 

 partial paralysis. There is no rudiment of an ovary in the $ -flowers (Fig. 3-40 

 A). The PERIANTH in the ? -flower differs from that of the $ in having the two 



