32 
ORGANOGRAPHY. 
BOOK I. 
dolle; and the reservoirs du sue joropre 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 ccecum 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 vittcB. Although 
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 Myrtacese, where they are called crypta, or glandulcB 
impresscB, or reservoirs vesicidaires, or glandes vesicidaires, or 
receptacles of oil. In the Pistacia Terebinthus the receptacles 
are tubular; in Coniferae 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 Ivfthehdlter of the Germans. Like the recep- 
tacles of secretion, the air cells have no proper membrane of 
their own, 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- 
