FOREST FORMATIONS OF THE ISTHMUS OF PANAMA 79 



of a few small islands, they are now lying at the bottom of the Gatun 

 Lake. All that is seen today along the road is secondary growth, often 

 of many years standing, but always characterized by the thick under- 

 brush, the abundance of Cecropia, Urera, and other groups of the 

 so-called tree-weeds, the relative absence of epiphytic plants, the climb- 

 ing sedges (Scleria) with blades as sharp as a razor's, and the extensive 

 fields of small or giant Heliconia. 



The real primary forest is found usually in parts removed from 

 roads or towns. It presents several types, according to the prevalence 

 of rainy or semi-dry climate, and in each case subdivisions can be 

 established on geological or topographical features, the latter including 

 such factors as altitude and combined sometimes with others — exposure, 

 change in temperature, etc. 



On the Atlantic watershed and in the interior of Darien we have 

 principally dicotyledonous rain-forests of the mesophytic type. Bamboo 

 thickets are rarely met with ; tree-ferns are scarce ; palms, better repre- 

 sented perhaps in the southern district, are never conspicuous or domi- 

 nating. This type of forest reaches its full development in the plain, 

 as, for instance, on the alluvial flats of Darien. On the hills the humus 

 layer is thinner, the humidity of the soil less, and the size of the trees 

 somewhat reduced. Some of these, however, rooted on hilltops or on 

 flat ridges, rival in size the giants of the plains. Such are, for instance, 

 the enormous, small-lea^■ed Monkeypot trees (Lccythis), which are 

 seen towering above the forest on the hills around Puerto-Obaldia on 

 the San Bias coast, or the Coumarouna trees of the foothills in the 

 Sambu Valley (Darien). A Monkeypot tree which I had felled to 

 obtain specimens near the place first mentioned measured 1.62 m. in 

 diameter at the base ; the trunk was 42 m. from the base to the crown 

 and the approximate total height was 55 m., or about 175 feet. In all 

 those tall trees the crown is umbrella-shape, with a single, terminal 

 story of very large, radiating limbs. In the trees of lesser size, filling 

 the space under the former, the crown is elongate, also with radiate 

 arrangement of the branches, which, however, are disposed in several 

 whorls. There is a great variety in the size and shape of the leaves, 

 but as a rule they are narrow in proportion to their length and long 

 tipped, and often pinnate or palmate ; in many cases also they are 

 bunched at the end of the branchlets, as, for instance, in the odd-looking 

 Cespedesia seemanni. with long, nude black limbs ending in enormous 

 bunches of obovate leaves about i m. long, from the middle of which 

 issues a no less immense spare raceme of brilliant yellow flowers. 

 Furthermore, in most trees of the evergreen rain-forest, the leaves are 



