HEVIEW. 117 



" From the same cause they Lave uo lateral buds— no branches. Buds 

 (which produce branches) originate from the soft and juicy parts of the tree 

 — but in endogenous trees this is surrounded by a thick hard compact casing 

 through which the buds cannot penetrate. Their only branches aro; the 

 splendid crown of leaves which proceeds from their one bud at the summit. 



"Hence the peculiar form of the palm trees, which present so striking- a 

 feature in the scenery of tropical climes, and form such a contrast with the 

 trees in more temperate latitudes ; raising a narrow unbranched stem often 

 to a height of about 150 feet, crowned by a magnificent cluster of leaves 

 many feet iu length bending elegantly outwards, and presenting altogether 

 oue of the most graceful objects which can adorn a landscape. From their 

 great height, which renders them tottering, and their manner of growth, 

 which causes them in time to become hard and compressed, even in the cen- 

 tre, so that they cannot transmit juices from the root, or new wood from the 

 leaves — the age of Palms is limited — perhaps not exceeding two or three 

 centuries at the utmost. 



'• Plants with endogenous stems have only one cotyleden (lobe) in the seed 

 (hence called rnonocotyledonous,) and have leaves with veins proceeding in 

 simple lines from the base to the summit, not forming a net-work as in the 

 leaves of the Lime tree, Cabbage, Primrose, &c Contrast, in this respect, 

 the plants just mentioned with the grasses, onion or lilly tribe. 



"Exogenous Stems. — The third class of stems consists of those in which 

 are observed concentric layers of vascular tissue, arranged symmetrically 

 round a central column ot cellular tissue, intersected by rays oi cellular tis- 

 sue proceeding from the centre towards the circumference, and enclosed by 

 a hollow cylinder of bark. 



" The Epidermis or Cuticle. — The epidermis is a thin membrane, resembling 

 much the cuticle of animals, and extending over the whole plant. It is des- 

 cribed as consisting of a layer of fine membrane provided with pores, and 

 covering a sort of cellular net-work. These pores open by an oval aperture, 

 surrounded by a small prominence (which is supposed to open or shut the 

 apperture as circumstances may require,) into the cellular net-work, in which 

 the vessels terminate. On the leaf the cuticle is a very important organ. 



" These pores or stomata give free passage to moisture. They are found 

 only on parts exposed to the air, and which evaporate freely. Roots, fleshy, 

 fruits, and seeds, and those parts of aquatic plants which are submersed, are 

 destitue of stomata. 



" The cuticle is supposed to protect the parts underneath from the too 

 direct action of air and water, to preyent too great evaporation of the fluids. 

 It affords little protection from heat or cold, except when covered by a thick 

 hair or wool as in the Great Mullein. On the trunks of the Fir, the Plane, 

 the Oak, and other trees, the office of the cuticle seems to be performed by 

 dead layers of bark, or of herbaceous integument, which are pushed out- 

 wards, having performed the functions for which they were made. 



" In forest trees and in the larger shrubs, the bodies of which are firm 

 and of strong texture, it is of little importance, except in the young and 

 tender state of the plant ; but in the reeds, the grasses, canes, and the plants 

 having hollow stalks, it is of great use, and is exceedingly strong ; and by 

 the microscope, seems to be composed of a grassy net-work, which is princi- 

 pally siliceous earth. This is the case iu the Wheat, in the Oat, in different 

 species of Equisetum, and above all in the Rattan, the epidermis of which 

 contains a sufficient quantity of flint to give light when struck by steel. The 

 siliceous epidermis serves as a support, protects the bark from the action of 

 insects, and seems to perform a part in the economy of these feeble vege- 

 table tribes, similar to that performed in the animal kingdom by the sell of 

 the crustaceous insects. I have ascertained, by experiment, that siliceous 

 earth generally exists in the epidermis of the hollow plants. 



To be Continued, 



