white man, has parted from the Indians
at their camping-place, no doubt after staying all night with them. Ha!
there's something at the back of all this; somebody behind Aguara and
his Indians--that very somebody I've been guessing at. He--to a dead
certainty."

The last sentences are not spoken aloud; for as yet he has not confided
his suspicions about Francia and Valdez to his youthful comrades.

"No matter about this shod horse and his back-track," he continues, once
more heading his own animal to the trail. "We've now only to do with
those that have gone forward, and forward let us haste."

While speaking he strikes his ponderous spurs against his horse's ribs,
setting him into a canter, the others starting off at the same pace.

For nearly an hour they continue this rate of speed, the conspicuous
trail enabling them to travel rapidly and without interruption. It
still carries them up the Pilcomayo, though not always along the river's
immediate bank. At intervals it touches the water's edge, at others
parting from it; the deflections due to "bluffs" which here and there
impinge upon the stream, leaving no room for path between it and their
bases.

When nearing one of these, of greater elevation than common, Gaspar
again draws his horse to a halt; though it cannot be the cliff which has
caused him to do so. His eyes are not on it, but turned on a tree,
which stands at some distance from the path they are pursuing, out upon
the open plain. It is one of large size, and light green foliage, the
leaves pinnate, bespeaking it of the order _leguminosae_. It is in fact
one of the numerous species of _mimosas_, or sensitive plants, common on
the plains and mountains of South America, and nowhere in greater
number, or variety, than in the region of the Gran Chaco.

Ludwig and Cypriano have, in the meantime, also drawn up; and turning
towards the tree at which Caspar is gazing, they see its long slender
branches covered with clusters of bright yellow flowers, these evidently
the object of his attention. There is something about them that calls
for his closer scrutiny; since after a glance or two, he turns his
horse's head towards the tree, and rides on to it.

Arrived under its branches, he raises his hand aloft, plucks off a spray
of the flowers, and dismounting, proceeds to examine it with curious
minuteness, as if a botanist endeavouring to determine its genus or
species! But he has no thought of this; for