30 
ORGANOGRAPHY. 
BOOK I. 
Sect. IV. Of spurious elementary Organs ; such as Air Cells, 
Receptacles of Secretion, Glands, S^c. Sfc. 
The kinds of tissue now enumerated are all that have as 
yet been discovered in the fabric of a plant. There are, 
however, several other internal parts, which although not 
elementary, being themselves made up of some one or other 
of the forms of tissue already described, nevertheless have 
either been sometimes considered as elementary, or at least 
are not referable to the appendages of the axis, and can be 
treated of more conveniently in this place than elsewhere. 
These are, 1. Intercellular passages; 2. Receptacles of secre- 
tion ; 3. Air cells ; 4. Raphides. 
1. Of Intercellular Passages. 
As the elementary organs are all modifications of either the 
spherical or cylindrical figure, it must necessarily happen that 
when they are pressed together, spaces between them will 
remain, which will be more or less considerable in proportion 
as the tissue preserves in a greater or less degree the cylindri- 
cal or spherical form. Wlien the pressure has been very 
uniform, as in the case of the tissue of the cuticle, and in many 
states of cellular substance, no spaces will exist. Wlien they 
do exist, they are called Intercellular passages (meatus or ductus 
intercellidares, canaux entrecellulaires). They necessarily follow 
the course of the tissue, being horizontal, vertical, or oblique, 
according to the direction of the angles of the tissue by which 
they are formed. Their size varies according to the size of 
the tissue and the quantity of sap. In plants of a dry charac- 
ter, they are frequently so small as to be scarcely discoverable ; 
w^hile in succulent plants they are so large as to approach the 
size of cells, as in the stem of Tropaeolum majus. (Plate II. 
fig. 14.) They are remarkably large in the horizontal parti- 
tions which separate the air cells of water plants. In Limno- 
charis Plumieri they exist in the form of little holes at every 
angle of the hexagons of which the partitions in that plant 
consist ; and are, no doubt, there intended as a beautiful con- 
