42 



DICOTYLEDONS 



as weapons against animals that would otherwise feed on them, 

 Protection is also afforded by an astringent acid, called tannin, 



Fig. 42. — Brancli oi Acacia 

 arabica, with legumes. 



\ 



contained in the bark. If the bark is damaged, 

 gum trickles out of it and covers the wound. 

 As the Acacia tree is one of the few plants that 

 grow in deserts, it can make good use of such 



means of defence. 



3. The Flowers (tig. 43) are small, but are 

 grouped in round heads. As the tree flowers in 

 desert regions and at such a time when there is 

 no rain, it can dispense with the many arrange- 

 ments by which, in other plants, the pollen of 

 the stamens is protected against bad weather. 

 Si) the tioral envelopes (calyx and corolla) are 

 considerably reduced (see fig. 43, c and k), and 

 tlie numerous stamens protrude widely from 

 them. In fact, the flower-heads look yellow from 

 the pollen only. 



4. The Legumes (Plate No. 628, 4) are flat 

 and narrow and depressed between the seeds. 



5. Uses for man. — The tree is useful in 



many ways. Tlie wood is very hard and can be employed for 



Fig. 4.'J. — Flower 



of tlic Acacia, 



k. Calyx c. Corolla. 



St. Stamens. 



(in. Anthers 



II. Stigma of style. 



(Much enlarged.) 



