LIFE OF THE PLANT-CELL. 81 



and gratuitous hypothesis to suppose that it possesses invisible pores, or 

 that the membrane stands in the same relation to fluid as salts to water. 

 In the latter case, the water is supposed to dissolve up a little of the mem- 

 brane, which, in passing through, it yields up again. The passing of the 

 fluid through the membrane is produced by the relation of water to certain 

 other substances contained in the cell. If gum or sugar is dissolved in 

 a small quantity of water, and pure water is poured carefully over the 

 solution, the two liquids remain apparently for a short time unmixed, but 

 at the edges where the fluids meet a process goes on, in which the two 

 fluids pass one into the other until the whole is completely mixed. If the 

 two fluids are separated by a vegetable or animal membrane, the attraction 

 is not diminished, because both fluids penetrate the membrane and thus 

 come in contact, but the thicker fluid passes through the membrane with 

 more difficulty than the thinner. Thus a larger quantity of the thin fluid, 

 in the same time, is found present with the thicker than of the thicker with 

 the thinner. The experiment may be performed in glass tubes, wh<.>n the 

 relative height to which the fluids will rise in a given time will be in pro- 

 portion to their relative thickness. The same results take place when 

 fluids, not thickened, but varying in specific gravity, as alcohol and water, 

 are employed, the lighter passing into the heavier most rapidly. Dutrochet 

 called the passing in of the thinner fluid endosmose, and the passing out 

 of the thicker exosmose, and measured the endosmotic power of the fluids 

 by the difference of height which they reached in tubes. By means of a 

 graduated apparatus, Dutrochet estimated the relative power of the fol- 

 lowing substances as compared with water : 



Animal albumen . . at 12 

 Sugar .... 1J 



Gum .... 5-17. 



Vegetable albumen belongs to the nitrogenous vegetable substances, and 

 is similar in many points to animal albumen. In its physical properties 

 it is difficult, if not impossible, to separate it from the vegetable substance 

 described above as mucus (protein). It appears to me not too much to 

 assume that this vegetable albumen (mucus), out of which the cytoblast is 

 formed, possesses the same endosmotic power as animal albumen. We can 

 thus easily explain how it is that, immediately after the cytoblast is sur- 

 rounded by a membrane, endosmose begins, and thus takes up those sub- 

 stances upon which the cytoblast exercises a changing influence. In this 

 ( way sugar and gum are formed, and the cell is thus filled with substances 

 which increase the process of endosmose. Scarcely any further explana- 

 tion of the process of absorption is needed, as this simple process suffices 

 for the understanding the most complicated phenomena of vegetable life. 

 It is to be regretted that so few experiments have been made on the 

 relations exhibited by this process. There are two points of especial im- 

 portance. The first is, the great variety in the nature of the various sub- 

 stances within and without the cells of plants, and the great difference in 

 the power with which they are attracted: on the relation of numerous 

 solutions to one another, we have no experiments. In the second place, 

 the nature of the separating membrane demands attention. Water and 

 alcohol, for instance, exhibit a very powerful reciprocal attraction ; but in 

 an endosmotic apparatus, when bladder or caoutchouc is used as a means 

 of separation, the result is very different. With the bladder the water 

 passes to the alcohol, but not vice versa, as alcohol does not easily per- 

 meate animal membrane. With the caoutchouc the result is exactly the 



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