UPON PLANT-HOUSES. 7'-^ 



exception of the Nopalese, are forest plants ; in the latter they 

 are the humbler vegetation, partly of forests,' but chiefly the 

 ground-vegetation of open places. 



In the second letter the writer enters into details concerning 



forest and open (Flur) vegetation. In tropical countries the trees 



are mostly of the former class, and rarely extend beyond their 



dense forests, which are constantly tending to expand their limits. 



Only few trees are so fond of light and impatient of shade as never 



to be found in forests ; as the Cashew-nut (Anacardium occi- 



dentale). The colossal constituents of forests, its oldest and 



longest enduring members, reach a height of 80 — 100 feet 



and upwards, and cause not only the most striking diminution 



of light, but also of temperature, which is higher than we usually 



find in our large plant-houses, namely, '22°, 28°, 30° R. and more. 



But of these trees only few ever find their way into our houses, 



and when there, they ai'e almost without exception the most 



thankless of all, inasmuch as they never produce flowers or fruit 



there. Who has ever seen a Tectona, Bertholletia, Lecythis, 



Caryocar, or any of the immense Vochysise, Qualese, Lauriuese 



or Leguminosse, which form the haute-voUe of such forests, in 



those states in our botanic institutions ? Though we find these 



often in the catalogues of the richest gardens, especially of 



France and England ; but they perish prematurely, or else they 



grow extremely slowly. Below the dense summit of the loftiest 



trees which form the dome of the forests, three other gradations 



may be observed, namely, the dicotyledonous trees, and climbers 



next in elevation, with several palms, which attain a height of 50 



to 80 feet; some of them, especially climbing plants, sometimes 



surmounting the dome itself. Of all these we possess many in 



our houses, but they blossom rarely. The second gradation is 



formed by low trees and shrubs, which we call underwood in our 



forests, such as numerous Leguminosse, Rubiacese, Euphorbiacete, 



Myrtaceae, Melastomaceae, Piperaceae, &c. These are still more 



in tbe shade than the preceding series, receiving light only 



laterally, when the sun is near the horizon, or accidentally from 



other causes. The last and lowest gradation consists of herbs, 



bulbs, grasses, Cyperacese, ferns, &c. Orchideae, Bromeliaceae, 



Aroideae, and other epiphytes, constitute here an essential 



feature. But whenever these primeval forests attain their fullest 



perfection, they consist in colossal trunks only, which have little 



or no underwood beneath the dense shade, the surface of the 



earth being at length deprived even of its grassy sod, and even 



