ACANTHACEAE 
219 
parenchymatous cells containing food-stuffs, and are eaten by the ants 
(cf. Cecropia). If any attempt be made to interfere with the tree 
the ants rush out and attack the intruder. A most efficient protection 
is thus afforded to this myrmecophilous A. (Cf. Cecropia, and 
see Nature , Aug. 1893, for an account of the leaf-cutting ants, the 
chief foes of the A.: and cf. Schimper, Pfianzengeog. pp. 147, 170. 
This was the first case of myrmecophily discovered ; see Belt’s 
Naturalist in Nicaragua.) 
A few A. are twiners, others hook-climbers (p. 172). Most sp. 
are xerophytes, often forming very characteristic features in the 
vegetation and scenery, eg. the Babul (A. arabica Willd.) with its 
low, spreading habit, is almost the only tree in many parts of the dry 
plains of India, and others are common in S. Afr. &c. 
The fir. (diagram, see order) has 00 long sta., affording little pro- 
tection to the pollen. In A. homalophylla A. Cunn. (S. E. Austr. ; the 
Myall) the seed hangs out on a long red funicle which may attract 
birds. 
Many A. yield valuable products. A. Senegal Willd. (Soudan) 
yields gum-arabic ; the gum exudes from the branches “ principally 
during the prevalence of the dry desert winds from the N. and E. 
which blow in the winter after the rainy season.” Other species yield 
inferior qualities of gum. A. catechu Willd. (E. Ind.) yields catechu 
or cutch (used in tanning), by digestion of the wood in hot water. 
A. deairrens Willd. (Austr.; black wattle) yields a good tan -bark ; 
inferior barks are yielded by A. pycnantha Benth. (S. E. Austr. ; 
golden wattle), A. dealbata Link (Austr. ; silver wattle) and others. 
The wood of many sp. is valuable, especially that of the Australian 
black-wood, A. melanoxylon R.Br. Many have sweetly scented firs. ; 
those of A. Farnesia?ia Willd. (trop.) are the Cassie flowers of 
perfumery. A. armata R.Br. (temp. Austr. ; kangaroo thorn). 
A. horrid a Willd. (S. Afr.) and others form good hedges or sand- 
binding plants. 
Acaena Linn. Rosaceae (ill. 9). 40 sp. S. Am., Mex., Polynes. 
Frt. hooked. Some sp. bud from junction of leaf and stalk. 
Acalypha Linn. Euphorbiaceae (A. 11. 2). 225 sp. trop. The anther 
lobes are curiously twisted. The stigmas are very large and branched. 
In A. mdica L. there are normal ? flowers at the base of the infl., 
then c? , and at the apex a single ? with only one ovule, whose seed 
has the radicle facing downwards and has no caruncle (Clarke). 
Several sp. are cultivated for their variegated leaves. 
Acampe Lindl. Orchidaceae (31). 10 sp. E. Ind., China, Afr. 
Acanthaceae. Dicotyledons (Sympet. Tubiflorae). 134 gen. with 1600 
sp., chiefly trop. but also Medit., U.S., Austr., &c. Many biological 
types occur — climbing plants, xerophytes, marsh plants, &c. — and 
there is much variety in habit. Trees are rare, most A. being shrubs 
or herbs with opp. exstip. leaves, usually thin and entire. Infl. 
most commonly a dichasial cyme, in its ultimate branchings tending 
