PROTOPLASM 19 



the vehicle of the physiological activity of the cell. The process of 

 nutrition and the other chemical changes included in the general 

 category of metabolism are carried on within the protoplasm, or at 

 any rate are initiated by the living substance. It is in the protoplasm 

 also that the interchange of energy occurs which becomes necessary 

 when translocation of material takes place, when movements are carried 

 out in connection with growth and in response to stimulation, when 

 external resistance is overcome, in fact, whenever work is performed 

 internally or externally by the plant or by one of its organs. Further, 

 that remarkable property of living organisms which the physiologist 

 calls irritability, likewise resides in the protoplasm. It is the living 

 substance that controls all the morphogenetic processes which impress 

 a specific character upon each cell as well as upon the entire plant. 

 Finally, it is the protoplasm which initiates and carries out all the 

 processes connected both with asexual and with sexual reproduction, 

 and which itself acts as the vehicle of the heritable characters of 

 the organism. 



Every protoplast must evidently be a highly complicated organism, 

 since an activity which is so excessively varied, but which is neverthe- 

 less governed by definite laws and characterised by the frequent 

 repetition of similar actions, demands a correspondingly complex 

 apparatus for its performance. 5 At first sight the normal condition 

 of the protoplasm, as revealed by its outwardly perceptible physical 

 characters, seems to be incompatible with the foregoing conclusion. 

 Generally speaking, protoplasm has a semi-liquid, slimy consistency ; 

 this fact has again and again given rise to an erroneous doctrine, which 

 refuses to admit the existence of the internal organisation that should 

 properly belong to a living substance and regards the protoplasm as 

 a complex liquid mixture or emulsion in the physical sense, within 

 which vital activity proceeds in a manner analogous to the purely 

 physical changes that may be observed in lifeless artificial solutions 

 and mixtures. 



A simile may help to explain how a substance, which superficially 

 appears to possess the properties of a semi-liquid material, and the 

 constituent particles of which are therefore readily displaceable 

 with reference to one another, may nevertheless be endowed with a 

 complicated internal structure and organisation. A great army 

 marching into the field is by virtue of its elaborate organisation capable 

 of executing the most varied and purposeful concerted movements and 

 actions ; its component divisions and subdivisions do not, however, 

 form a rigid structure, but are on the contrary in the highest degree 

 mobile relatively to one another. This internal mobility may indeed 

 apparently develop into complete disintegration in the case of skirmishes 



