THE SKELETON OF THE PLANT 49 



considerable internal strain, the micellae attracting each 

 other and tending to squeeze out the water. The latter, on 

 the other hand, tends to separate the micellae. 



According to Strasburger, the molecules of the solid 

 matter are held together by chemical affinity, and there is 

 no definite aggregation of them into micellae. He pictures, 

 therefore, a linkage of the atoms into a molecular network, 

 the meshes of which are occupied by water. On either 

 hypothesis the quantity of water is capable of considerable 

 increase or diminution, and the wall can be made to swell 

 up by causing it to imbibe more fluid. This can be brought 

 about by exposing it to the action 

 of strong mineral acids, such as 

 sulphuric acid. The water is held, 

 however, by the solid particles 

 with very great tenacity. 



A different view of the composi- 

 tion of the cell-wall was advanced 

 some years ago by Wiesner. He 

 held that the substance of the 

 membrane as it is first formed FlG> 4 2.-THicKENED CELLS OF 



Consists Of rOWS Of granular bodies WoOD > SHOWING STRATIFICA- 

 , . . 7 TION. (After Sachs.) 



which he termed dermatosomes ; 



these are connected together by protoplasm which surrounds 

 them. He based his view on the phenomena which accom- 

 pany the disintegration of the wall by the action of strong 

 alkalies. On this hypothesis the cell- wall is living while 

 young and growing. The protoplasm exists in it between 

 particles of solid matter, and it holds the water in its 

 substance. 



The thickening which always supervenes to a greater 

 or less extent upon the first formation of the cell- wall is 

 brought about by the protoplasm in a way similar to the 

 method of its original construction. Layers composed like 

 the original one are continually secreted by the protoplast, 

 and are deposited upon its exterior in apposition with the 

 wall already there. Hence walls which have a perceptible 



4 



