ARTIFICIAL CELLS. 215 



a great extent exaggerated \ If, for instance, a drop of concentrated solution of 

 chloride of copper is placed in a vessel filled with yellow prussiate of potash, a closed 

 precipitation membrane of ferrocyanide of copper is instantaneously produced on 

 the contact of the two fluids : there thus arises a cell-like structure, and, since the 

 precipitation membrane is permeable to the water of the surrounding solution, this 

 penetrates into the cell, attracted by the chloride of copper in the interior. The 

 increase in volume effects a corresponding pressure on the very thin precipitation 

 membrane, which, since it is not extensible, bursts after a time ; it is, however, at 

 once completed again to a closed membrane, since the two salts come in contact 

 for a moment at the gaping fissure, and at once produce a new precipitation 

 membrane. In this way such a cell may gradually grow considerably. Somewhat 

 greater is the similarity of the growth of a precipitation membrane of gelatine 

 tannate, formed when a drop of non-gelatinising solution of glue is placed in a 

 solution of tannin. Such a cell grows more uniformly and without the violent 

 eruptions referred to above. How far this growth may be compared with that 

 of a living vegetable cell, even with reference to the molecular processes in the 

 membrane, depends, however, upon our knowledge of the growth of true vegetable 

 cells. Here we have only to do with turgescence, and it is obvious from what 

 has been said that in these artificial cells the turgescence depends upon properties of 

 the membrane other than in the natural ones. 



The capability of becoming turgescent is one of the most important properties 

 of the vegetable cell, since a long series of vital phenomena depend entirely or in 

 part upon it. In the first place, the fact is to be insisted upon, that growth and the 

 increase in circumference generally of living vegetable cells only take place when 

 they are turgescent, a point to which I shall return later in the theory of growth. 

 The opposite of the turgescent condition of a vegetable organ is that of drooping. 

 Every one knows that cut-off leaves or branches, if not placed with the cut surface 

 in water, soon become flaccid ; the shoot-axes, previously stiff" and brittle, become 

 highly flexible, and are no longer able to support the weight of the leaves, which 

 have likewise become flaccid — the parts sink down : they droop. If the whole 

 was previously weighed in the fresh state, it may be easily demonstrated that the 

 drooping shoot has become lighter : it has given off" water by evaporation, and it is 

 simply this loss of water, by which the turgescence of the cells has become 

 diminished, which causes the drooping, since if the shoot is allowed to take up 

 water (which of course does not always succeed to a sufficient extent), the drooping 

 condition disappears, and the young shoot-axes and leaves again become tense and 

 rigid, because the cells again become turgescent. With the consideration of this 

 phenomenon we come to the important question, upon what does the stiff'ness and 

 elastic rigidity of the succulent parts of plants depend.? a question which here 

 requires still closer consideration. 



' Traube, the discoverer of the so-called precipitation membranes and the artificial cells con- 

 sisting of them, studied the properties of the latter, and thereby added to our knowledge of the 

 processes of diffusion, upon which I wrote critically in detail and on the basis of my own researches 

 in my ' Lehrlmch der Botanik; III Aufl., 1873. Traube's unfounded claims to priority as the 

 founder of the theory of growth by intussusception, and the astonishing confusion of his artificial 

 precipitation cells with actual vegetable cells, I replied to in 1878 in the 'Bot. Zeitung,' p. 308 

 (^' Zur Geschichte der viechanischcit Theorie des Wachstltnins der organischen Zellen ). 



