THE MOLECULAR FORCES IN PLANTS. 139 



1 See Detmer, Landicirthschl. Jtihrliicht'r, Bd. 10, p. 733. 



2 See Detmer, Wollny's Forschungen auf dem Gebiete der Agriculturphysik, 

 Bd. 5, p. 253. 



3 See Detmer, Botan. Zeitung, 1886, No. 30. 



4 See Loew, Flora, 1892, H. 3, pp. 374 and 386. 



III. MOLECULAR PROCESSES IN PLAJSTTS. 



56. Imbibition. 



We prepare a delicate transverse section through the stem of 

 a young Laminaria. On examination of the section in alcohol, 

 but little is to 'be seen of the details of structure. They stand 

 out clearly, however, on addition of water. We distinguish an 

 outer cortex, the cells of which possess brown membranes, and 

 the so-called inner cortex which forms the main mass of the 

 tissue, and of which the cell-membranes are colourless. In the 

 middle of the section we observe the medullary tissue, consisting 

 of tubular cells. If we mount sections of Laminaria in alcohol, 

 and then introduce water from the edge of the cover-glass, we 

 can readily determine by microscopic examination that at the 

 moment of absorption of water the sections increase considerably 

 in volume. We can also prove the increase in volume by taking 

 the dimensions of a piece of Laminaria stalk with a millimetre 

 scale, on the one hand when dry, and on the other after saturation 

 with water. The substance of Laminaria is therefore capable of 

 swelling by absorption of water, and the process by which this is 

 brought about is termed Imbibition. The increase in volume of 

 pieces of Laminaria placed in contact with water does not, how- 

 ever, proceed indefinitely, but is limited in extent, and this is 

 of considerable importance, because it teaches that a piece of 

 Laminaria and organised plant structures in general behave in 

 the same way when placed in water at the ordinary temperature 

 behaves very differently from, say, gum. 



If a piece of a Laminaria blade, whose weight in the dry state 

 is known, is laid in water, and after lapse of definite intervals of 

 time (e.g. every eight minutes) removed from it, dried with 

 blotting-paper, and weighed, it will be found that the absorption 

 of water by the object during such periods is at first rapid, gradu- 

 ally diminishes, and finally ceases. If we suspend the soaked 

 piece of Laminaria in the air by means of platinum wire, and 



