Development, and Structure of the Vegetable Cell. 418 
will be applied, especially during the dissolution of the ciliary 
membranes, so as to promote or produce in the adjoining region 
the predisposition to take on the function of a root. 
Those germ-cells (gonidia) which are clothed with a uniform 
ciliary epithelium, as, for example, those of the genus Vaucheria, 
display no such polar tendency at their opposite ends. 
On the other hand, similar conditions are encountered in 
the developing germ-cells of the complex organization of pha- 
nerogamous plants. In these also the mystery of the nor- 
mal position of the radicle of the young plant with regard to 
the micropyle (independently of the mode of attachment of the 
ovule to the placenta, from which it receives its nourishment) 
will undoubtedly find its partial solution in the fact that the first 
impulse to the assumption of the typical form of the mature 
organism, which is innate in the fertilized cell, is derived from 
the contents of the pollen-sac, which penetrates into the ovule 
through the micropyle and determines the polar property of the 
indifferent germ-cell. 
In the filiform Conferve, this polar property of the germ- 
cell, when once set up, propagates itself to every cell, in series, 
throughout the organism, and is equally stamped upon every 
single cell in it ; and the same thing takes place in the Phanero- 
gamous plants which are composed of various kinds of tissues, 
by which we may explain the predisposition to polar activity 
inherent in every fragment of the stem or leaf, which manifests 
itself im the normal development of new roots at the originally 
inferior extremity of the organic fragment. 
The desire to make this phenomenon dependent on the pre- 
sence of vessels which are endowed with functions analogous to 
those of animals (which, curiously enough, has been quite recently 
again put forward) arises from a complete misconception of the 
structure of the tissues of plants. 
g IV. 
The joint-cells of Cladophora are at a certain period filled with a tissue 
composed of secretion-cells, which arise along the middle of the cells 
and extend themselves to the periphery, where they dissolve.—Some of 
these secretion-cells have their membranes thickened. 
According to the opinion now generally received, most of the 
tissue-cells of plants consist, at a certain period of their life, of 
an external membrane, a primordial utricle (second cell-wall 
inwards), a nucleus containing a nucleolus (the third and fourth 
inner cell-walls), and between the nucleus and primordial utricle 
a considerable amount of cloudy, granular, mucilaginous fluid— 
the protoplasm, plasma, or cell-juice. In this last, durmg the 
enlargement of the two outer cell-walls, irregularly disposed 
