338 Proceedings of the 



ties of the leaves and the aerial canals of the petiole, M. Dutrochet 

 plunged a leaf of the Nymphcea lutea into a glass vessel filled with 

 water, leaving the severed extremity of the petiole out of the water. 

 On placing the vessel under the receiver of an air-pump, and ex- 

 hausting the air, he did not see any air issue from the submerged 

 parts of the leaf; and on re-admitting the air into the vessel, a quar- 

 ter of an hour afterwards, the lower part of the leaf retained its whitish 

 tint, which proved that it had not lost the air which in its natural 

 state filled its aerial cavities. M. Dutrochet then recommenced the 

 experiment with the same leaf, taking care to submerge it entirely ; 

 and as soon as he began to exhaust the air, numerous air-bubbles 

 escaped from the severed extremity of the petiole, but none from 

 the edge or border of the leaf. When, however, the air was re-ad- 

 mitted, a quarter of an hour afterwards, the lower surface of the leaf 

 instantly lost its whitish tint and became as green as the upper sur- 

 face ; thus proving that the air had entirely escaped from the aerial 

 cavities through the petiole, and that these cavities had become filled 

 with water. 



The hair or nap which is frequently found on leaves, particu- 

 larly the lower surface, is considered by M. Dutrochet as being 

 filled with air, and as forming the respiratory conduits of the nerves 

 over which they are placed, while the stomata are seen in the inter- 

 vals left between those nerves. In the rose-laurel the lower surface 

 has no stomata, but is covered entirely with nap or hair. 



The aerial tubes of the Nymphcca are slightly hexagonal, and 

 from the angles spring hairs, which, being of the same height in 

 the different united tubes, form for each ternary system of tubes the 

 starry figure noticed by M. Amici. M. Dutrochet considers these 

 hairs as conduits which, by their capillarity, absorb the air contained 

 in the canals and carry it into the vegetable tissue, in the same man- 

 ner as the ramifications of the trachea in insects do into every part of 

 the living animal. Other plants offer different dispositions, but all 

 are calculated to absorb the air from the aerial cavities and carry it 

 into the most remote parts of the plant. It results, therefore, from 

 the experiments of M. Dutrochet, that in every part of plants there 

 are aerial organs, filled with a gas compounded of oxygen and azote 

 in variable proportions, but in which the oxygen is always in a 

 smaller proportion than in the atmospheric air, which proves that it 

 has been absorbed by the interior organs of the plant. The same 

 circumstance is observed in analysing the air contained in the tra- 

 chea of insects, which proves that their mode of respiration is the 

 same ; that is to say, the transport of respirable elastic air into all 

 their parts. But the origin of this air is not quite the same, since 

 insects derive it wholly from the atmosphere, while the plants gene- 

 rate a considerable part of it in their tissue by the influence of light. 

 The azote, which is not absorbed in the internal respiration of the 

 plants, is necessarily expelled ; and, in fact, we perceive that flowers 

 exhale a great deal of azote while they absorb oxygen, particularly 



