4 
ORGANOGRAPHY. 
BOOK I. 
which it hes, and to which it usually adheres; but occasionally 
elongates less rapidly, when it is broken into minute portions, 
and is carried along by the growing membrane. In direction 
it is variable (Plates I. and II.); sometimes it is straight, 
and attains a considerable length, as in some fungi; some- 
times it is short and straight, but hooked at the apex, as in the 
lining of the anther of Campanula ; occasionally it is straight, 
and adheres to the side of membrane, as in the same part 
in Digitalis purpurea ; but its most common direction is spiral. 
Whether it is solid or hollow has not been fully demonstrated ; 
Purkinje asserts that it is hollow, as will be hereafter men- 
tioned; but there can be no doubt that it is also, at least 
sometimes, solid, as in the fibrous bladders of the leaf of Onci- 
dium altissimum ; it is the opinion of many that it is hollow 
in the case of spiral vessels. Elementary Fibre has a constant 
tendency to anastomose, in consequence of which reticulated 
appearances are frequently found in tissue. Slack adds that 
it sometimes branches. 
The forms under which the elementary organs are seen are, 
1. Cellular tissue; 2. Woody tissue; and, 3. Vascular tissue. 
It is almost certain that all these forms are in reality modifica- 
tions of one common type, namely, the simple cell, however 
different they may be from each other in station, function, or 
appearance. For, in the first place, we find them all developed 
in bodies that originally consisted of nothing but cellular tissue ; 
a seed, for instance, is an aggregation of cells only ; after its 
vital principle has been excited, and it has begun to grow, woody 
tissues and vessels are generated in abundance. We must, there- 
fore, either admit that all forms of tissue are developed from the 
simple cell, and are consequently modifications of it; or we must 
suppose, what we have no right to assume, that plants have a 
power of spontaneously generating woody and vascular tissue 
in the midst of the cellular. Mirbel has lately reduced the first 
of these suppositions to very nearly a demonstration ; in a 
most admirable memoir on the developement of Marchantia he 
speaks to the following eflPect. ' I at first found nothing but a 
mass of tissue composed of bladders filled with little green balls. 
Of these some grew into long slender tubes, pointed at each 
