398 NOTES OF A BOTANIST 
The species of Sclerolobium are not usually 
riparial, but one species [S. odo7'atissimitm, sp. n.) 
is eminently so, constituting a great ornament of 
the shores and islands of the Rio Negro towards 
the mouth of the Casiquiari, and perfuming the 
whole breath of the river with the abundance of its 
pale yellow honey-scented flowers ; and it is notable 
that this is the only species of the genus in which 
I have found sacciferous petioles. The sac is large, 
extending upwards from the knee of the petiole to 
the base of the second pair of leaflets, and it has a 
furrow along the upper face. 
I presume the ants have been induced to take 
up their residence on these particular trees on 
account of the abundance and long persistence of 
their honied flowers. On other species of Sclero- 
lobium, inhabiting dry lands solely, such as ^S. tincto- 
7nu7n, Benth., and 5^. pmiinLlattLni, Vog., I have seen 
the flowering panicles infested with little fire-ants, 
which, however, seemed to have their permanent 
habitation in the ground, about or near the tree- 
roots, and never to perforate the leaf-stalks. Many 
other Leguminosae, especially the woody climbing 
Phaseoleae, are visited by ants when in flower, and 
knobs or galls caused by the perforation of those 
insects are frequent on the panicles of Dioclea 
and allied genera ; [but I have not remarked any 
instance of such knobs having become hereditary, 
except in Ptei^ocarpus ancylocalyx, Benth., a small 
tree on the banks of the Solimoes or Upper Amazon, 
which has the rachis of the racemes thickened in 
the middle, the swelling being sometimes (but not 
always) tenanted by ants]. 
In the shrubby Cassias, which are common weeds 
