THE DICOTYLEDONES 



1661 



wing-like, with the odd petal erect. In Cassia all five petals are spreading 

 and more or less equal. Cercis siliqiiastruni is the only species of the genus 

 which is at all commonly cultivated in this country where it is easily 

 recognized by the purple-red flowers, which appear on the tree before the 

 leaves. It is known as the Judas Tree because it is said that Judas Iscariot 

 hanged himself on one. There are five species, distributed in north tem- 

 perate regions. None of the other genera is commonly cultivated in Britain. 

 The Mimosaceae are characterized by minute, actinomorphic flowers, 

 in close clusters, with long coloured stamens (Fig. 1521), and by thin bipin- 

 nate leaves. They occur in the tropics and subtropics, often in dry or semi- 

 desert regions. The most important genus is Acacia, which includes some 



Fig. 1 52 1. — Acacia sp. A, Flower. B, Longitudinal section. 



550 Species which are known under the general name of Wattles, especially 

 in Australia, where some 300 of the species occur. Many species do not 

 develop their pinnate leaves during the early stages of seedling development 

 and the petioles become phyllodes. In many species stipules develop as 

 large spines. In the Central American A. sphaerocephala these are inhabited 

 by ants, which bore in and remove the entire internal tissue. Extra floral 

 nectaries are developed on which the ants feed. If the tree is harmed the 

 ants rush out to protect it. 



Many species of Acacia are of economic importance. A. Senegal, which 

 occurs in the Sudan, yields the best Gum Arabic, which is exuded from the 

 branches during dry desert winds. A. catechu is a native of the East Indies. 

 It yields catechu or cutch which is employed in tanning and is prepared by 

 digesting the wood in hot water. Several species produce barks which are 

 used in tanning; that of A. decurrens, an Australian tree known as the Black 



