32 ORGANOGRAPHY. BOOK I. 



dolle ; and die reservoirs du sue jpropre of the last author. 

 To this class also are to be referred the turpentine vessels^ and 

 the milk vessels of Grew; the reservoirs accidentels of De Can- 

 dolle ; and also the reservoirs en cceeum of the latter, which are 

 the clavate vessels of oil found in the coat of the fruit of Um- 

 belliferae, and which are commonly called vitta. Altliough 

 the receptacles of secretion have no proper coat, yet they are 

 so surrounded by cellular tissue, that a lining or wall is 

 formed, of perfect regularity and symmetry. The tissue of 

 this lining is generally much smaller than that of the neigh- 

 bouring parts. In figure, the receptacles are extremely vari- 

 able, most commonly round, as in the leaves of the Orange 

 and of all Myrtaceae, where they are called crypta, or glandidce 

 impi'essce, or reservoirs vesiculaires, or glandes vesicidaires, or 

 receptacles of oil. In the Pistacia Terebinthus the receptacles 

 are tubular; in Coniferaj they are very irregular in figure, 

 and even position, chiefly forming large hollow cylindrical 

 spaces in the bark. Those in the rind of the orange and 

 lemon are little oblong or spherical cysts ; their construction, 

 which is very easily examined, gives an accurate idea of that 

 of all the rest. (Plate II. fig.. 21.) 



3. Of Air Cells. 



Besides the common intercellular passages, and the recep- 

 tacles now described, there is another and a very remarkable 

 sort of cavity among the tissue of plants. This is the air 

 cell; the lacuna of Link, the reservoir d'air and cellule d'air of 

 Kieser, and the liifthelidlter of the Germans. Like the recep- 

 tacles of secretion, the air cells have no proper membrane of 

 their oami, but are built up of tissue; and this sometimes takes 

 place with a truly wonderful degree of uniformity and beauty. 

 Each cell is often constructed so exactly like its neighbour, 

 that it is impossible to regard it as a mere accidental dis- 

 tension of the tissue : on the contrary, air cells are, in those 

 plants to the existence of which they are necessary, evidently 

 formed upon a plan which is uniform in the species, and 

 which has been wisely contrived by Providence in that man- 



