THE GENERAL CHEMISTRY AND PHYSICS OF PLANT-LIFE. 267 



imbibition each micella surrounds itself with a layer of water 

 of a given thickness ; in complete desiccation the micellae lie in 

 contact ; in general their form is polyhedral. If water enters 

 between the micellae it indicates that the attraction or cohesion 

 between water-molecule and micella must be greater than the 

 attraction of the micellae for each other ; according to Nageli 

 the attraction between water-molecules and micellas decreases 

 more rapidl}^ with the distance than does the mutual attraction 

 of the micellae ; after a time the latter Avill predominate : this is 

 the point of maximum imbibition. (Reinke's experiments show 

 what enormous forces are exerted by the processes of imbibition 

 in such organized bodies. Swelling of the cell-walls of Lami- 

 naria indicated a pressure of forty atmospheres.) 



2. Every normal cell-membrane which has passed its earlier 

 stages of development is, as a rule, doubly refractive. According 

 to Bkucke, Nageli, Schwendener, and Ambkonn, the cause of this 

 is to be found in the arrangement of the crystalline, anisotropic, 

 smallest particles, the micellce. The membranes of typical me- 

 chanical cells with normal extensibility undergo no change in 

 their optical behavior due to pressure or extension. Membranes 

 of great extensibility when they are subject to tension show an 

 increase in the interference of light-rays. It may be probable 

 that in the latter case the optical difference is due to a reticular 

 arrangement of the micellae (Schwendener). If such is the case 

 it is in favor of the theory of " anisotropic micellae " (Meyer, 

 1895). 



V. Ebner and others, and in partial agreement with them, 

 ZiMMERMANN, suppose the cause of this double refraction of some 

 cell-membranes, to lie in the systematic arrangement of isotropic 

 micellae, without, however, being able to give any definite expla- 

 nation for such systematic arrangement. The evidence in sup- 

 port of this supposition is based upon the observation made on 

 the above-mentioned highly extensible cells, without including 

 any substances not pertaining to our subject, as bones, cartilage, 

 etc. 



In reference to the " molecular tensions " which voN Hohnel 

 assumes to exist and which are supposed to cause the phe- 



mass Is called a pleon (" Pleone"). The micellce are either simple aggregates of 

 molecules or pleon-aggregates. 



