Development, and Structure of the Vegetable Cell. 413 



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 

 indifi*erent germ-cell. 



In the filiform Confervse, 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 in 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. 



§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, granulai*, mucilaginous fluid — 

 the protoplasm, plasma, or cell-juice. In this last, during the 

 enlargement of the two outer cell-walls, irregularly disposed 



