CHAP. I. 
CELLULAR TISSUE. 
7 
riddled full of holes {Jig. 2.)^ the aperture of which 
does not exceed the of a millimetre (or of 
half a line) ; or are less frequently pierced with 
transverse slits, which are occasionally 
so numerous as to transform the bladders 
into a real articulated tissue, as in the 
pithof the Nelumbium {fig. 3.)." This 
statement is now well known to have 
been founded upon inaccurate observation ; what the 
supposed pores really are has already been explained. 
p. 3.) 
With reference to this subject, it may be also observed, that 
the bladders often contain air-bubbles, which appear to have 
no direct means of escape, and that the limits of colour 
are often very accurately defined in petals, as, for instance, in 
the stripes of tulips and carnations, which could not be the 
case if cellular tissue were perforated by such holes as have 
been described ; for in that case colours would necessarily run 
together. 
One of the most striking instances with which I am ac- 
quainted, of cellular tissue having the appearance of pores, is 
in Calycanthus, where it was pointed out to me by Mr. Va- 
renne. (Plate I. fig. 1.) But even in this, a careful ex- 
amination with, glasses of different magnifying powers shows 
that the apparent pores are certainly not such, but composed of 
a solid substance, which may be distinctly seen by varying the 
direction of the rays of the transmitted light with which it 
is viewed. Sometimes they appear like luminous points ; by 
a little alteration of light they acquire a brownish tint ; and if 
seen with the highest powers of a compound microscope, where 
there is a great loss of light, they become perfectly opaque. 
Cellular tissue is always transparent and colourless, or at 
most only slightly tinged with green. The brilliant colours 
of vegetable matter, the white, blue, yellow, scarlet, and other 
hues of the corolla, and the green of the bark and leaves, is 
not owing to any difference in the colour of the bladders, but 
to colouring matter of different kinds wliich they contain. 
In the stem of the Garden Balsam (Impatiens balsamina), a 
single cell is frequently red in the midst of others that are 
B 4 
