592 
VAUGHAN MACCAUGHEY 
Lyngbya cladophorae Tilden. 
Phormidium papyraceum Gomont. 
Schroederia setigera Lemm. 
Scytonema guyanense Bornet. 
Martensiana Menegh. 
Mougetia capucina Ag. 
Nostoc foliaceum Mougeot. 
ocellatum Lyngb. 
rivulafe Borzi. 
varium Kuetz. 
verrucosum Vaucher. 
Oedogonium crispum var. Haviense 
Phormidium favosum Gomont. 
Nordst. 
Oedogonium spp. 
Oscillarotia sancta Kuetz. 
formosa Bory. 
Spirogyra spp. 
Spirulina major Kuetz. 
Stigeoclonium tenue Kuetz. 
Tolypothrix distorta Kuetz. 
Ulothrix minulata Kuetz. 
17. RAVINES 
Between the grassy ridges specified as "zone two" of the valley 
head are deep, narrow, steep-walled ravines, lying between the 700- 
and 1,400-ft. contours. These ravines are not to be confused with the 
hanging valleys, which occupy a higher level — 1,400 to 2,000 feet — 
and are mantled with the true rain-forest vegetation. The ravines 
are occupied by plants of the lower forest zone. These narrow, humid 
gorges are the regions of minimum illumination in the valley. Their 
floors receive no direct sunlight until an advanced hour of the morning. 
The eastern arc of the sky is shut out by the mountain wall. These 
ravines are so narrow — their streamways are but 8 to 15 feet wide — 
that sunlight can enter only directly from above, and from the front, 
i. e., facing the main valley. The subdued illumination is augmented 
by the cloud-cap that lies across the summit ridge. The gloominess 
contrasts strikingly with the glare of the main valley floor. 
The larger arborescent species that are most prevalent in the 
ravines are: Aleurites moluccana, Eugenia Malaccensis, Charpentiera 
ovata, Pipturus albidtis, Urera Sandwicensis , Elaeocarpus bifidus, 
Clermontia macrocarpa. 
Under the shade of these trees occur a number of smaller species 
that are characteristically shade tolerant, for example: Lysimachia 
Hillebrandii, Rollandia grandifolia, R. lanceolata, Cordyline terminalis, 
Smilax Sandwicensis, Oplismenus compositus, Zingiber Zerumbet, 
Alocasia, Colocasia, Dioscorea spp., Curcuma, Musa, Touchardia lati- 
folia, Crepis japonica, and many pteridophytes. 
The plants that grow in these cool, humid, shady, protected ravines 
are sharply contrasted, from the ecological standpoint, with those 
that inhabit the hot, arid, glaring, windswept foothill slopes. These 
two habitats represent two environmental extremes. 
