396 M. S. B. Scliuetzlei- on the Aeriferom 



In the lake of Escoubous, situated upon the summit of the 

 Hautes-PyreneeSj at 2032 metres above the level of the ocean, 

 there lives a very remarkable variety of Eamincidus aquatilis. 

 It forms a sort of very extended turf, moored to the bottom of 

 the water by the radicles which shoot out even at the extremity 

 of its stems — side by side with broad carpets of a blackish-green 

 colour, formed by Tremelloid UIvje. Here, in opposition to the 

 laws which cause aquatic plants to seek the open air in order to 

 flower and accomplish the act of reproduction, it remains con- 

 stantly immersed, far from the margins, where the severity of 

 the frosts might destroy it, and far from the great depths, where 

 it would no longer find the light necessary for its vegetation'^"; 

 here it expands its finely divided leaves and its white corollas 

 with their golden bottoms, and here it is fecundated and repro- 

 duces itself without ever attempting to reach the surface. The 

 ])0ssibility of fecundation is shown by a bubble of air produced 

 during the work of vegetation and retained between the petals 

 before their full expansion, in which the anthers project their 

 pollen (Guerin, Diet. d'Hist. Nat. tome viii. p. 465). 



The evohxtion of gas in closed cavities, which we observe in a 

 certain number of aquatic plants before the expansion of the 

 flower, is evidently in relation to what it has been agreed to call 

 vegetable respiration. During this operation the plant not only 

 takes carbonic acid from the air or water, but it also absorbs, 

 through all its parts, oxygen, which combines with the carbon 

 of certain vegetable matters to form carbonic acid. The chemical 

 action of the solar light induces the decomposition of the car- 

 bonic acid absorbed, as well as of that formed in the plant. The 

 carbon is tixtd in the ])lant by combining with the elements of 

 water, nitrogenous matters, &c. The oxygen is evolved. The 

 stomata appear to play an important part in respiration; never- 

 theless, according to the investigations of Duchartre, there is no 

 definite relation between the number and size of the stomata 

 and the quantities of gas evolved by plants when exposed to the 

 sun. In certain trees which have a dry and leathery texture 

 there is an inverse ratio between the considerable number of the 

 stomata and the weakness of the evolution of gas. Moreover 

 what proves that the gases exhaled by plants are not evolved 

 solely through the stomata is, that we see them issue from the 

 cells of the epidermis of the upper surface of leaves in plants in 

 which this surface has no stomata, when the leaves are immersed 

 in water. AVe have already demonstrated a similar evolution 

 from the immersed leaves of Utricidaria . In entirely submerged 

 aquatic plants the leaves are destitute of stomata, and absorption 



* The plant in question does not occur citlicr at the margin or at great 

 depths, because it cannot exist in either of these positions. 



