392 Miscellaneous Intelligence. 



when moistened, and open to light and dry air; because roots and 

 plants living under water have them not, floating leaves have them 

 only on their upper surface ; and because (with reference to rain and 

 dew) they are more abundant on the under surface of leaves, than on 

 the upper. Tiiat they are not intended for evaporation is assumed, 

 because the plant being separated from the root they close, although 

 evaporation still goes on. That they are not excretory organs, ap- 

 pears from their corresponding with cavities containing neither fluid 

 nor solid matter. It is therefore concluded that they are intended 

 for the passage of air, but whether for its entrance or exit is difficult 

 to determine. At night when the large pores of the epidermis are 

 closed, the leaves absorb the carbonic acid dissolved in the dew, whilst 

 by day when they are open, the same leaves decompose the gas ; 

 hence, perhaps, they may be destined, M. Amici thinks, to the emis- 

 sion of the oxygen gas resulting from this decomposition ; an opinion 

 favoured by the remark of M. De Candolle, that the corolla which 

 has no pores produces no oxygen. 



Mode of UnioninthevcgetableStructure. — It has been a question whe- 

 ther the vessels of plants are all constructed of one continuous and single 

 membrane, or whether each vessel has a complete membrane of its 

 own. M. Amici in examining this point has not only ascertained the. 

 latter to be the case, and shewn that the membrane between two 

 vessels is in consequence always double, as well at the diaphragms 

 as at the sides ; but has shewn that they frequently are really sepa- 

 rated, having curved surfaces and spaces between them : these inter- 

 vals never contain any thing but air, and they put the existence 

 of the vasa revehentia of Hedwig, and the meatus intercellulures of 

 Link beyond doubt. 



On the Air Vessels of Plants. — M. Amici considers every vessel 

 or vacuity whatever may be its form, tubular or cellular, in which the 

 microscope discovers oriiices, or openings more or less long, as air 

 vessels. This class comprehends the spiral vessels, the false trachse, 

 the porous tubes, the vessels with false partitions, those with small 

 crowns, those with false cells, and a great variety of others. A recent 

 section of a plant shews these vessels empty and dry, and very dis- 

 tinct from the fibrous vessels, and the cells containing their re- 

 spective juices ; and if the section be put under water, air is seen to 

 issue from them. 



There are cases when the elastic fluid in these vessels cannot have 

 been obtained from the atmosphere, as in the caulineafragilis, which 

 grows under water. The author thinks it possible that the small 

 crowns discovered in the interior of the sap vessels, may, perhaps, 

 be the organs by which the air is in these cases separated from the 

 water. 



It is a constant law in the general system of vessels, that those 

 which are fibrous surround those which arc aeriform. In ligneous 

 plants nature has substituted other channels for the intercellular pas- 



