Vor. I] STEWART—BOTANY OF THE GALAPAGOS ISLANDS 219 
Lianes occur in the following genera: Argyreia, Asclepias, 
Boussingaultia, Canavalia, Cardiospermum, Cuissampelos, 
Cissus, Elaterium, Galactea, Ipomoea, Momordica, Mucuna, 
Passiflora, Phaseolus, Rhynchosia, and Sicyos. Most of these 
are herbaceous. 
Those plants which attain the size of trees are included in the 
following genera: Acacia, Acnistus, Avicennia, Bursera, 
Cereus, Conocarpus, Erythrina, Hibiscus, Hippomane, Opun- 
tia, Piscidia, Pisonia, Psidium, Prosopis, Rhizophora, Sap- 
mdus, Scalesia, Solanum, and Zanthoxylum. More than one 
half of these are confined to the regions below the moist, con- 
trary to the general belief that the lower parts of the islands 
support only a low and bushy vegetation outside of the arbor- 
escent cacti. A few of the above attain sufficient size to be of 
economic importance for lumber, among which the species of 
Erythrina, Psidiwm, and Sapindus are the most important. 
The greater number of species of plants have small and 
rather inconspicuous flowers, a fact that has been mentioned by 
other travelers who have visited the islands. There are a few 
plants, however, that possess rather showy flowers. Such are 
comprised in the genera Argyreia, Cacabus, Cereus, Cordia, 
Datura, Erythrina, Gossypium, Hibiscus, Ipomoea, Kallstroe: 
mua, Miconia, Mucuna, Nicotiana, Opuntia, Parkinsonia, Passi- 
flora, and Tribulus. Most of these genera include species of 
wide distribution. By far the largest number of endemic spe- 
cies have very small flowers, a fact that may be due to the 
relatively small number of species of insects on the islands. 
EcoLoGIcAL FACTORS 
W ater 
Great differences in the amount of precipitation are often 
found within short distances on the Galapagos Islands, some- 
times within a change of elevation of two or three hundred feet. 
The lower parts of the islands adjacent to the shore are as a 
rule very dry and only receive moisture in any considerable 
quantities during about three months of the year, while the 
middle and upper parts are quite moist most of the time. 
Between the two extremes of moisture there are all sorts of 
gradations. 
