CHAP. I. 
CELLULAR TISSUE. 
13 
47,000,000,000 cellules ; so that, supposing it to have gained 
its size in the course of twelve hours, its bladders must have 
developed at the rate of near 4,000,000,000 per hour, or of 
more than sixty-six millions in a minute. 
Cellular tissue grows for a long time after its generation, 
and hence the bulk of a given part may be much in- 
creased without the addition of any new elementary organs. 
Link states that in the branch of a Pelargonium cucullatum 
about 1 line in diameter, he found the larger cells 2 V ®f a line 
broad, which, in an older branch of the same plant, 2 lines 
in diameter, the larger cells were of a line broad; hence 
it was evident that the growth of the branch depended upon 
the growth of the individual cells. 
The bladders of cellular tissue are always very small, but 
are exceedingly variable in size. The largest are generally 
found in the gourd tribe (Cucurbitaceae), or in pith, or in 
aquatic plants ; and of these some are as much as the of 
an inch in diameter ; the ordinary size is about the or 
the and they are sometimes not more than the yq\jq. 
Kieser has computed that in the garden pink more than 
5100 are contained in half a cubic line. 
Cellular tissue is found in two essentially different states, 
the membranous and the fibrous. 
Membranous Cellular Tissue is that in which the sides 
consist of membrane only, without any trace of fibre; it is 
the most common, and was, till lately, supposed to be the 
only kind that exists. This sort of tissue is to be considered 
the basis of vegetable structure, and the only form indispen- 
sable to a plant. Many plants consist of nothing else ; and 
in no case is it ever absent. It constitutes the whole of 
Mosses, Algae and Lichens ; it forms all the pulpy parts, the 
parenchyma of leaves, the pith, medullary rays, and principal 
part of the bark in the stem of Exogens, the soft substance 
of the stem of Endogens, the delicate membranes of flowers 
and their appendages, and both the hard and soft parts of fruits 
and seeds. 
It appears that the spheroid is the figure which should be 
considered normal or typical in this kind of tissue ; for that is 
the form in which bladders are always found when they are 
generated separately, without exercising any pressure upon 
