1901.] NATURAL SCIENCES OF TfllLADELPHIA. 557 



officinalis L. and Laguncularla racemosa Gaertn. Pistia stratiotes 

 L. floats iu the fresh- water streams of the island, or loosely 

 attached to the soil along their banks. Sagittaria lancifolia L. 

 may also be classed as a hydrophyte. 



Mesophytes. — The plants composing the vegetation of a tropical 

 forest are in superimposed layers, or stories. The different levels 

 at which tropical plants grow is in direct response to the environ- 

 mental conditions of light and moisture. These storied layers 

 may be termed vegetal strata. It may be staled, iu this con- 

 nection, as axiomatic, that in a tropical forest, when one ascends 

 from the ground to the crowu of the dominant forest trees, as the 

 light increases the moisture content ot the air decreases. On the 

 ground in the forest, mosses, ferns and fungi abouud in the deep 

 shadow and growing in the mould arising from fallen leaves and 

 rotting Avood. In the forests, on the trees, ferns, aroids and orchids 

 are found, while serpent-like lianes clamber from limb to limb 

 and from tree to tree, uutil they reach abundant light in the 

 crowns of the trees above. Epiphytes and parasites, more or less 

 xerophytic in habit, are found iu the tops of the dominant species 

 of trees. 



Forest Vegetation. — The richness of the tropical flora and the 

 lush growth of the vegetation iu general is most marked in those 

 situations that are exposed to the copious rains that fall during the 

 summer months. The drenching rainfall, the richness of the soil 

 in the mountain valleys and coastal plains are such as to encour- 

 age to the highest degree a luxuriant fern and arboreal vegetation. 

 Along the banks of streams occur Bamhusa vulgaris Schrad. , 

 Heliconia sp. , Amomuni sp., and of the palms, Oreodoxa oleracea 

 Mart., Thrinax argentea Lodd, 2\ ^xf/'ivy/ora Sw., Acroeomia 

 sclerocarpa Mart., Euterpe oleracea Engelm. 



The component vegetation of damp Avoods consists of Musa 

 sapientiim L. , 31. coecinea Andr., Heliconia bihai L., H. psitta- 

 corum L., Arundo occidentalis Sieber, Canna edulis Ker-Gawl, 

 Sivietenia mahagoni Jacq., Hmnatoxylon carapecJiianum L., Madura 

 tinctoria D. Don., Cedrela odorata L., Artocarpus incisa L., 

 Chrysophyllum cainito L , Catalpa longisshna Sims, Sloanea dentata 

 L., Swartzia tomentosa D.C., Ilex obcordaia Sw., Ceerojjia pieltata 

 L., and other arborescent species. The larger trees are draped 

 by lianes of the following species: Passiflora caerulea L., P. lauri- 



