418 
HOBTIOtTLTUEAI. DII'EICUTIES. 
paintings ; and that small cakes of this substance were 
sold at the great market of Tenoehtitlan. But a colouring 
matter, chemically identical, may be extracted from plants 
belonging to neighbouring genera; and I should not at 
present venture to affirm that the native indigoferse of 
America do not furnish some generic difference from the 
Indigofera anil, and the Indigofera argentea of the Old 
World. In the coffee-trees of both hemispheres this 
difference has been observed. 
Here, as at the Bio Negro, the humidity of the air, and 
the consequent abundance of insects, are obstacles almost 
invincible to new cultivation. Everywhere you meet with 
those large ants that march in close bands, and direct their 
attacks the more readily on cultivated plants, because they 
are herbaceous and succulent, whilst the forests of these 
countries afford only plants with woody stalks. If a mis- 
sionary wishes to cultivate salad, or any culinary plant of 
Europe, he is compelled as it were to suspend his garden in 
the air. He fills an old boat with good mould, and, having 
sown the seed, suspends it four feet above the ground with 
cords of the ehiquichiqui palm-tree; but most frequently 
places it on a slight scaffolding. This protects the young 
plants from weeds, worms, and those ants which pursue their 
migration in a right line, and, not knowing what vegetates 
above them, seldom turn from their course to climb up 
stakes that are stripped of their bark. I mention this cir- 
cumstance to prove how difficult, within the tropics, on the 
banks of great rivers, are the first attempts of man to &»$pro- 
priate to himself a little spot of earth in that vast domain 
of nature, invaded by animals, and covered by spontaneous 
plants. 
During the night of the 13th of May, I obtained some 
observations of the stars, unfortunately the last at the Cas- 
siquiare. The latitude of Mandavaca is 2° 4' 7 " ; its longi- 
tude, according to the chronometer, 69° 27'. I found the 
magnetic dip 25 '25° (cent, div.), showing that it had increased 
considerably from the fort of San Carlos. Tet the sur- 
rounding rocks are of the same granite, mixed with a little 
hornblende, which we had found at Javita, and which as- 
sumes a syenitic aspect. We left Mandavaca at half-past 
two in the morning. After six hours’ voyage, we passed on 
