618 



BOTANY 



PART II 



all Leguminosae have alternate, compound, stipulate leaves. Many 

 are provided with pulvini (Figs. 239, 240), which eftect variation 

 movements of the leaves and leaflets. 



Family 1. Mimosaeeae. — Trees, and erect or climbing, shrubby 

 plants with bipinnate leaves. Flowers actinomorphic, pentamerous or 

 tetramerous. ^^stivation of se2:)als and petals valvate. Stamens 

 free, numerous, or equal or double in number to the petals. The 

 colour of the flower is due to the length and number of the stamens, 

 the corolla being as a rule inconspicuous. The pollen grains are often 

 united in tetrads or in larger numbers. The flowers are grouped in 

 spikes or heads. Embryo straight in the seed. 



Important Genera. — There are no representatives native to Europe of this 

 family, whicli is abundant in the tropics. The Sensitive Plant {Mimosa pudiea) 





Fig. 634. — Acojahx sphaeroccphala. I, Leaf and part of stem ; S, hollow thorns in which the auts 

 live ; F, food bodies at the apices of the lower pinnules ; N, nectary on the petiole. (Reduced.) 

 II, Single pinnule with food-body, F. (Somewhat enlarged.) 



(Fig. 240) occurs as a weed throughout the tropics and exhibits great irritability 

 to contact (cf. p. 323). Numerous species of the genus Acacia are distributed 

 through the tropics and sub-tropics of the old and new worlds ; some are in cul- 

 tivation in the Mediterranean region. The Australian forms of tlie genus are 

 frequently characterised by possessing ]ihyllodes (Figs. 17-1, 183), the vertical 

 position of which contributes to the peculiar habit of the Australian forests. Only 

 the seedlings of these species have a few bipinnate leaves which constantly succeed 

 the cotyledons. Some American species of ylcacia are inhabited by ants (Fig. 634) 

 which live in the large stipular thorns and obtain food from Belt's food-bodies at 

 the tips of the pinnules. A mutual symbiosis is as little demonstrated as in the 

 case of Cecropia adenopus (cf. p. 556). Many species of Acacia are of considerable 

 economic value owing to the presence of gums and tannins in the cortex or in the 

 heart-wood. A. catechu (F"ig. 633) and A. sicma are East Indian trees from which 

 Catechu is obtained. 



Official. — By the disorganisation of the i)arenchyma of the stem of Acacia 



