64 PLANT PHYSIOLOGY 



ture which distinguishes all of these from physical properties is 

 this: they are not static, but dynamic, and, moreover, are inde- 

 pendently, internally, spontaneously, or auto dynamic. They 

 might, therefore, be more properly described as powers, rather 

 than as properties. It is the manifestations of their activity in the 

 substance forming their physical seat which constitute the phe- 

 nomena of life; and it is their interaction with the kinetic forces 

 of external nature which develops organic structure and habit. If 

 it shall ultimately be found that there is any feature in Protoplasm 

 not existent in inorganic nature, it is probably connected with 

 the power of self -regulation, which is the most remarkable and 

 distinctive of all the attributes of the living substance. 



The physical properties of any substance, Protoplasm in- 

 cluded, are believed to reside in its molecules, which are the units 

 of physical structure. It is not logically conceivable that in 

 Protoplasm both the physical and the vital properties reside in 

 the same units, and hence investigators have had to assume also 

 a unit of vital structure (plasom, etc.), presumably larger than the 

 molecules and aggregates of them, a subject with which the 

 student should make himself acquainted through the literature. 

 Incidentally it is noteworthy that this logical necessity involves 

 the assumption of a distinctive chemical Protoplasm. 



Correlated with this subject is the consideration of (a) the 

 phylogenetic origin of Protoplasm, a matter on which we have 

 no knowledge and little rational, speculation; (b) spontaneous 

 generation; (c) the distribution of Protoplasm in space and 

 range of temperature. Upon the state of knowledge of these 

 matters the student should also inform himself. 



LITERATURE. The subjects of this section are comprehensively 

 treated in VERWORN'S "General Physiology" and in PFEFFER'S 

 "Physiology." There is a classification of vital properties in the 

 chapter introductory to VINES' "Lectures." The most thorough 

 dicussion of the units of protoplasmic structure and properties is 

 WIESNER'S " Die Elementarstructur und das Wachsthum der lebenden 

 Substanz" (Wien, 1892). 



