How Plants Draw in Various Materials 



177 



for one another, somewhat as a magnet and its armature are 

 held together by magnetism; and this explains why the mem- 

 brane, although composed wholly of separate units, holds to- 





Fig. 59. — A diagram illustrating the construction of membranes. The circles are water; 

 the smaller squares are molecules, and the larger are micellae, of wall substance, a, rep- 

 resents a dry membrane (which always contains some water) and b, a saturated mem- 

 brane, supposed to be seen in section, reduced to only a few micellae. 



gether as a solid. At the same time the micellae possess a still 

 stronger affinity for something quite different, namely water, 

 which accordingly they can draw in as thin films among and 



