CHAP. I. 
INTERCELLULAR PASSAGES. 
37 
until they enter the hairs of many plants, in which they form 
a plexus of excessively fine vessels. 
In the lowest orders of plants, and in some others, they are 
wholly wanting. They are largest in plants having milky 
juice, and smallest in those whose juice is transparent. 
Plate II. contains representations of several laticiferous 
vessels. Fig. 13. and 18. shows them in the capillary 
state in the hairs of plants. Fig. 16. shows them thin-sided 
and filled with latex. Fig. 17. represents them thick-sided 
and filled with latex. Fig. 19. shows them empty. At 
fig. 12. Of, and they are seen parallel with the other tissue, 
filled with latex, and a little contracted at intervals. 
Sect. VI. Of spurious elementary Organs ; such as Air Cells, 
Receptacles of Secretion, Glands, ^c. ^c. 
The kinds of tissue now enumerated are all that have as 
yet been discovered in the fabric of a plant. There are, 
however, some 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 secretion ; 
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. When the pressure has been very 
uniform, as in the case of the tissue of the cuticle, and in many 
states of cellular substance, or when elementary mucus holds 
the tissue together completely, no spaces will exist. When 
D 3 
