AGRICULTURAL BOTANY. 261 



by a septem or partition of a porous character. This we find in the roots. The fluid in their 

 interior is rendered denser than the water around by an admixture of the descending sap ; and 

 the spongiole (or spongelet) supplies the place of a partition. Thus, then, as long as this dif- 

 ference of density is maintained, the absorption of fluid may continue. But if the rise of the 

 sap is due to the action of endosmose, there ought also to be an exosmose. This is found to 

 take place ; for if a plant is grown with its roots in water, the fluid surrounding them is soon 

 found to contain some of the peculiar substances they form, and which are contained in the 

 descending sap. Thus a pea or bean would discharge a gummy matter ; a poppy would com- 

 municate to the water an opiate impregnation, and a spurge would give it an acrid taste. 



"Thus we see how beautifully and how simply this action, extraordinary as it seems, is 

 accounted for, when its whole history is known on principles which operate in other depart- 

 ments of nature." — Dr. Carpenter. 



From this it must appear obvious to every one that, to keep plants in a healthy state, the 

 conditions of endosmose and exosmose must be carefully maintained. Thus in the case of 

 bulbs maturing and at rest, and of plants cut down in the autumn, such as Pelargoniums and 

 Fuchsias, the action of the leaves being destroyed, the fluid, rising by the force of endos- 

 mose, must gradually subside, and the plants languish into a state of semi-vitality, till such 

 time as genial warmth shall expand the fluid within their latent buds, and cause them to open 

 and put forth new leaves. This is the reason why the application of water to plants thus cir- 

 cumstanced should be carefully avoided, excepting, indeed, a few special subjects, whose suc- 

 culency is not sufficient to keep them from being shrivelled up. 



Tropical Scenery of the Amazon. 



Mr. Wallace, a recent traveller in South America, gives us the following highly instruc- 

 tive and well-stated estimate of tropical vegetation. He says — 



" There is grandeur and solemnity in the tropical forest, but little of beauty or brilliancy 

 of color. The huge buttress trees, the fissured trunks, the extraordinary air-roots, the 

 twisted and wrinkled climbers, and the elegant palms are what strike the attention and fill 

 the mind with admiration and surprise and awe. But all is gloomy and solemn, and one 

 feels a relief on again seeing the blue sky and feeling the scorching rays of the sun. 



" It is on the roadside and on the rivers' banks that we see all the beauty of the tropical 

 vegetation. There we find a mass of bushes, and shrubs, and trees of every height, rising 

 over one another, all exposed to the bright light and the fresh air, and putting forth, within 

 reach, their flowers and fruit, which, in the forest, only grow far up on the topmost branches. 

 Bright flowers and green foliage combine their charms, and climbers with their flowery fes- 

 toons cover over the bare and decaying stems. Yet, pick out the loveliest spots, where the 

 most gorgeous flowers of the tropics expand their glowing petals, and for every scene of this 

 kind We may find another at home of equal beauty, and with an equal amount of brilliant 

 color. 



"Look at a field of buttercups and daisies, — a hillside covered with gorse and broom, — a 

 mountain rich with purple heather, — or a forest-glade azure with a carpet of wild hyacinths, 

 — and they will bear a comparison with any scene the tropics can produce. I have never 

 seen any thing more glorious than an old crab-tree in full blossom ; and the horse-chestnut, 

 lilac, and laburnum will vie with the choicest tropical trees and shrubs. In the tropical 

 waters are no more beautiful plants than our white and yellow water-lilies, our irises, and 

 flowering rush ; for I cannot consider the flower of the Victoria regia more beautiful than that 

 of the Nymphoza alba, though it may be larger ; nor is it so abundant an ornament of the tro- 

 pical waters as the latter is of ours. 



" But the question is not to be decided by a comparison of individual plants, or the effects 

 they may produce in the landscape, but on the frequency with which they occur, and the pro- 

 portion the brilliantly-colored bear to the inconspicuous plants. My friend Mr. R. Spruce, 

 now investigating the botany of the Amazon and Rio Negro, assures me that by far the greater 

 proportion of plants gathered by him have inconspicuous green or white flowers ; and, with 

 regard to the frequency of their occurrence, it was not an uncommon thing for me to pass 



