340 THE PH ILADELPHIA FLORIS T. [No. 11 



** posed of cells. The cells of those air-roots possess a thin transparent^] 

 membrane, and contain mucilage with all those particles, the presence c/ 

 of which in the cavities has been ascertained by microscopic anj 

 chemical observation. They are nitrogenous particles, dextrine, 

 sugar, all dissolved with mucilage in water. The absorbent organs 

 are chiefly the outermost and tenderest cells. They are of great 

 consequence to the plant. By the action of endosmose they absorb 

 from the ground water and divers earthy particles, so far as they are 

 soluble in water, and the nature of those particles and of the mem- 

 brane of the cells permit their admission into the cavity of the cell. 

 Besides, they take up particles which are produced by decomposition 

 of animal substances, and the remains of vegetables in the ground. — 

 The latest researches prove most satisfactorily, that with the water 

 which is in the ground, several salts, of lime, potash, soda, and even 

 salts of metals, as well as gases, carbonic acid, ammonia, are taken 

 into the plant, by means of the peculiarly formed extremities of the 

 roots, which are called spongioles, in the cells of which are never 

 found either incrustation or openings; and which, notwithstanding 

 the absence of the latter, are, however, perfectly pervious. The 

 surface of the root branches does not absorb any liquid, nor does the 

 surface of the trunk root itself. 



Quite otherwise is the case with the alimentary parts of the so- 

 called air-Orchids. Their exterior is white as snow, dry, the surface 

 smooth, and for the most part not divided or branched ; transparent, 

 and more or less sappy only near the point. They grow to a remark- 

 ably great length, and rarely attain the thickness of a quill. 



If these roots be cut in a cross direction, and the slice carefully 

 examined by the aid of a microscope, a very singular state of the 

 web of the cells will be perceived. What should be called the bark 

 of the root is in this, one would say, a kind of papery tissue, which 

 covers the air-root externally ; each cell is literally filled with spiral 

 threads or fibres of an extraordinary fineness. Whereas in the usual 

 web of cells the greatest diameter is in the length of the cell ; in this 

 the breadth much exceeds the length. Now, in all other cells of 

 plants, which are exposed to the light and air, we meet with many 

 particles which are considered as the produce of the growth of the 

 plant, united with those of the atmosphere and the light (among which, 

 e. g. y the globules of a green color have a principal place) ; but in 

 these we find the cells quite empty, except of the fibres, which run 

 in all directions, and frequently cross each other. More inwards fol- 

 lows the simple web of the cells, and lastly, the fibrous part of the 

 roots, in the middle of which, again, cells are found. These roots 

 must be, naturally, well calculated to imbibe moisture, which they 

 ^require in great measure ; and, in case they are not continually ex- 



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