CONDITION OF AGGREGATION OF ORGANISED STRUCTURES. 597 



Traube maintains that there is no such thing as an endosmotic equivalent in the 

 sense of the older theory. Endosmose is independent of any interchange, since it 

 results entirely from the attraction of the dissolving substance for the solvent; and 

 this attraction is invariable at the same temperature and may be termed Endosmotic 

 Force. The endosmotic force of grape-sugar, for instance, is very great, that of gela- 

 tinous substances very small. 



To these researches, which are of extreme importance in reference to vegetable 

 physiology, and of which we shall make much use in t)ie sequel, though with a cautious 

 selection, Traube has added observations on the growth of the pellicle-precipitates of 

 copper fcrro-cyanide, the main results of which however I have been unable to confirm 

 after a number of experiments. 



If a drop of a very concentrated solution of copper chloride is dropped into a 

 dilute solution of potassium ferro-cyanide, it immediately becomes coated with a thin 

 brownish pellicle of copper ferro-cyanide which exhibits peculiar phenomena. It is 

 more convenient to place small pieces of copper chloride in the ferro-cyanide solution, 

 where a green drop is immediately formed at the expense of the water of the solu- 

 tion, producing the pellicle on its surface, and still enclosing the solid copper chloride 

 which dissolves gradually from the permeation of the water. These cells manifest active 

 growth and a variety of differences not easy to explain and dependent on secondary 

 circumstances; some have very thin pellicles, are roundish, and exhibit a slight tendency 

 to grow upwards ; they usually form a number of small wart-like outgrowths and attain 

 very considerable dimensions (from i to 2 cm. in diameter). They appear to be formed 

 chiefly by the solution of large pieces of the copper chloride. Others have thick reddish 

 brown pellicles, grow quickly upwards in the form of irregular cylinders, rarely 

 branch, and attain a diameter of from 2 to 4 mm. and often a height of several cen- 

 timetres. Combinations of the two forms also occur which sometimes form a kind of 

 horizontal tuberous rhizome-like structure from which long stalk-like outgrowths arise 

 upwards, and root-like protuberances downwards. 



It is impossible, in the space at our disposal here, to give a detailed description 

 of these phenomena ; one only may be specially mentioned :— that these pellicles of 

 copper ferrocyanide do not grow, as Traube supposes, entirely by intussusception, 

 but also in quite a different way (by eruption). When a brown pellicle has been 

 formed round the green drops, water penetrates quickly from without through the 

 pellicle to the copper chloride ; this becomes rapidly stretched, and, as may be clearly 

 seen, at length ruptured. The green solution immediately escapes through the fissure, 

 but becomes at once coated with a pellicular precipitate which appears either as an 

 intercalated piece of the previous one, or as an excrescence or branch of it, a process 

 which is repeated as long as any copper chloride remains inside the cell. We cannot 

 therefore in this case conclude that deposition of fresh molecules of the pellicle takes 

 place between those already in existence. These cells cannot, so to speak, be injured ; 

 if they are pricked, then at the moment when the point which pricks them is with- 

 drawn an outgrowth follows immediately, which is easily to be explained from what has 

 been said. In consequence of the rapid flowing in of water through the perforation, the 

 dissolved or the still solid copper chloride has no time to form a homogeneous solution ; 

 a stratification arises which begins in the lower part of the cell with a very concentrated 

 solution, and passes in the upper part into almost pure water when the cell has already 

 grown to some height. Since the dilute upper fluid is lighter than the surrounding 

 solution, it exerts an upward pressure upon the membrane-just as a cork held down 

 under water attempts to rise— till it is ruptured below or at the apex (in the second 

 form of cell). But the lighter fluid, when on the point of ascending, becomes at once 

 surrounded by a pellicle which remains attached to the walls of the fissure of the old 

 one; and thus apical growth takes place in cells of this description m the form of 

 eruptions, just like the formation of branches and excrescences in the round ones. If 

 the fluid in the upper part of the cell is pure water, large pieces of the pellicle break off" 



