134 FAMILIES OF FLOWERING PLANTS 
“mesquite” of Mexico and the southwestern States; the two species 
occurring within our borders differ strikingly in their fruits, one (P. 
pubescens) having the pods twisted like a corkscrew, so that it is known 
as screwbean. The true mesquite (P. juliflora), has long flattened pods 
containing “beans” or seeds: which are an important article in the 
dietary of the average Mexican. 
The very large genus Acacia is represented in all tropical coun- 
tries. A peculiar feature of its morphology is that the usually decom- 
pound leaves, consisting of many leaflets, are in nearly all the Hawaiian 
and Australian species reduced to flat bodies known as phyllodes, which 
‘look exactly like ordinary sim- 
ple leaves, though somewhat 
coriaceous (leathery) in tex- 
ture, and standing vertical in- 
stead of horizontal. The most 
important economic product 
yielded by the genus is gum, 
particularly gum-arabic; also, 
the drug known as catechu. 
Both these articles are derived 
from the refined juice or sap. 
Adenanthera pavonina, the red 
sandalwood of tropical Asia, is 
one of the most valued timber 
trees of that region. Its bright 
scarlet seeds, oddly enough, 
are very uniform in weight, 
each being 4 grains, and they 
are therefore extensively used 
by Oriental jewelers as weights. 
While the shrubs and trees of 
From Coulter’s Plant Structures. Copyright, 1900, D this family are not extensively 
Appleton & Co, grown in our greenhouses, they 
Fig. 116. A sensitive plant (Acacia), showing the f : tant it : 
flowers with numerous stamens, and the pinnately orm a very lmportant 1tem In 
compound leaves, After Meyer and Schumann, tropical landscape gardening, 
and in congenial situations they are of great size and beauty. The 
group is probably more conspicuous in Australia than in any other 
country. 
Family Caesalpiniaceae. Senna Family. Herbs, shrubs or trees, 
comprised in about 90 genera and 1000 species, chiefly of tropical dis- 
tribution. They are distinguished by the nearly regular, often rosa- 
ceous flowers, with 5 sepals and 5 petals, the upper or odd petal en- 
closed by the lateral ones; stamens 10 or fewer; fruit a pod. 
