398 NOTES OF A BOTANIST CHAP. 



The species of Sclerolobium are not usually 

 riparial, but one species (S. odoratissimum, 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 ,5. tincto- 

 ri inn, Benth., and 5". paniculatum, 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- 



o 



roots, and never to perforate the leaf-stalks. Many 

 other Leguminosas, 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 Pterocarpus 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 



