16 
ORGANOGRAPHY. 
BOOK I. 
Instead of being very rare, cellular tissue of this kind 
appears to be found in various parts; it has been already 
mentioned as existing in the leaves of Sphagnum ; it is also 
found in the pith of Rubus odoratus. I originally discovered 
it in the parenchyma of the leaves of Oncidium altissimum, 
and in the coat of various seeds. Mr. Griffith has detected it 
abundantly in the aerial roots of Orchidaceous plants, -where 
in fact it is extremely common in numerous species, and 
Purkinje has shown, by a series of excellent observations and 
drawings, that it constitutes the lining of the valves of almost 
all anthers. The forms under which it exists in these parts 
are far more various than those of membranous cellular tissue. 
The principal varieties are these : — 
A. Membrane and Fibre combined. 
" 1. Fibres twisted spirally, adhering to a spheroidal or angu- 
lar membrane, and often anastomosing irregularly, without the 
spires touching each other. (Plate I. fig. 12.) This is what 
is found in Oncidium altissimum leaves, in the aerial roots of 
some Orchidaceous plants, in the lining of many anthers, and 
is what Mohl has figured ( Ueber die Poren, ^c. tab. i. fig. 9.), 
from the pith of Rubus odoratus. It approaches very nearly 
to the nature of spiral vessels, hereafter to be described, and 
appears only to be distinguishable by the spires of the fibres 
not being in contact, being incapable of unrolling, having no 
elasticity or tenacity ; and by the bladders not being cylin- 
drical and tapering to each end, but spheroidal. It is easily 
examinable in Pleurothallis ruscifolia, and forms upon the 
side of the cells elevations which give them a beautifully pitted 
appearance when cut across. In the subcutaneous parenchyma 
of the leaves of this plant the fibres of one cell are placed ex- 
actly opposite those of the next cell, so that sections of the 
walls exhibit double depressions and elevations all along the 
line, so regular that, unless a very good microscope is used, 
they appear to form open passages from one cell to the 
other. 
2. Fibres crossing each other spirally, and forming a reti- 
culated appearance by their anastomosing within oblong blad- 
