:ll 



" It will be recollected probably, that the author made some 

 casual observations on this subject, in a previous paper. 

 Since that time he had paid much more attention to it, and 

 was enabled to lay before the Society many new facts and 

 experiments. 



"The valisneria spiralis, on which the observations were 

 chiefly made, is a grass-like, aquatic plant, found in the south 

 of France. It is for the most part submerged, having no 

 floating leaves, and is propagated chiefly by runners. It is 

 with difficulty procured in England, and some care is required 

 to preserve it through the winter. 



"When a leaf of this plant is submitted to microscopic 

 examination, it is found to consist of an assemblage of cells 

 of irregular size and shape, all of which contain a quantity 

 of transparent mucus, a bright, large, soft globule, or nucleus, 

 and from twenty to two hundred smaller bodies, round and of 

 a green colour, to which the name of chlorophyll has been 

 given. 



"The cells are divisible into two classes — those composing 

 the epidermis, or outward coating of the leaf; and those con- 

 tained in the interior, or parenchyma. The former are small 

 and irregular in shape, being usually 300 or ,Ju inch square, 

 and rarely approacliing to the figure of a parallelogram. The 

 latter are usually elongated, and built up together not unlike 

 the bricks in a wall; their long diameter varies from 1^ to 

 the bo of an inch, their short from uic to zU inch. 



"Each cell is perfect and complete in itself; but all are 

 all more or less united to each other, that they may possess 

 the necessary cohesion as a whole. Where no union exists 

 the interspaces are filled up by the oxygen and other gaseous 

 products, secreted by the plant. These interspaces do not 

 exist in the epidermis, and it is worthy of remark, that the 

 circulation is found in it for a shorter and more uncertain 

 duration than in t lie parenchyma, where they are so abundant. 

 In the chara vulgaris, in which the circulation is found as 



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