10 
ORGANOGRAPHY. 
BOOK I. 
have developed at the rate of near 4,000,000,000 per hour, 
or of more than sixty-six millions in a minute. 
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 3^^^, and 
they are sometimes not more than the ttjoo* Kieser has 
computed that in the garden pink more than 5100 are con- 
tained in half a cubic line. 
Cellular tissue is found in three essentially different states, 
the membranous, the Jihrous, and the vasiform. 
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 indispens- 
able to a plants Many plants consist of nothing else ; and 
in no case is it ever absent. It constitutes the whole of Mosses, 
Algae, Fungi, Lichens, and the like; 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 01 
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 issue ; for that is 
the form in which bladders are always found when they are 
generated separately, without exercising any pressure upon 
each other ; as, for example, is visible in the leaf of the white 
lily, and in the pulp of the strawberry or of other soft fruits, 
or in the dry berry of the jujube. All other forms are con- 
sidered to be caused by the compression or extension of such 
spheroids. 
When a mass of spheroidal bladders is pressed together 
equally in all directions, rhomboidal dodecahedrons are pro- 
duced, which, if cut across, exhibit the appearance of hexa- 
gons. (Plate I. fig. 12.) This is the state in which the tissue 
