BOOK III. 



PHYSIOLOGY. 



CHAPTER I. 

 MOLECULAR FORCES IN THE PLANT. 



Sect. i. — The Condition of Aggregation of organised structures \ 

 Cell-walls, starch-grains, and protoplasmic structures consist, in their natural con- 

 dition, at every point that can be seen even under the microscope, of a combination 

 of solid material with water. If these organised structures are placed in a sub- 

 stance capable of removing water, a part of their aqueous contents is withdrawn; 

 while, on the other hand, if they are in contact with aqueous solutions possessing 

 certain chemical properties and of a proper temperature, they absorb more w^ater. 

 The volume alters with the change in the proportion of water ; loss of water causes 

 contraction, absorption of water a corresponding augmentation of volume. Since 

 the absorption of water occasions a considerable elevation of temperature (air-dry 

 starch rises 2° or 3° C. when mixed with water of the same temperature), it must 

 be supposed that the water contracts as it is absorbed^. Within certain limits 

 these variations in the proportion of water may occur without occasioning any per- 

 manent change in the molecular structure ; but if, with a higher temperature and in 

 the presence of chemical reagents, the proportion falls below a certain minimum 

 or exceeds a certain maximum, permanent changes of the internal structure take 

 place which can no longer be reversed ; and the internal organisation of the body 

 becomes partially or entirely destroyed. 



' See Sachs, Handbuch der Experimental-Physiologie, p. 398 '^ seq.^mgdi u. Schwendener, 

 Das Mikroscop, vol. II, p. 402 e( seg.; compare also Book I of this work, p. 31 et sey.— Cramer, 

 Naturforsch. Gesells. in Zurich. Nov. 8, 1869. 



2 Jungk, in Pogg. Ann. 1865. vol. 125, p. 292 et seq. 



