237 



Bacterium Pasteurianum V7as omitted r/hen the temperature was too 

 JigJ (p. '^1) * Thus the living cytoplasm can permanently for- 

 feit it« activity for certain processes, as in our first example, 

 or its capacity for reaction to certain (external and internal) 

 stimuli is again made possible so soon as the disturbing- effects 

 of the unsuitable temperature are removed - aa In our second 

 example (see above) , 



Ho absolutely certr,in case is known as yet in which abnormal 

 temperature conditions can cause the formr-tlon of abnormal tis- 

 sue in any way other than by the arrestment of certain processes. 

 In Prlllieux's experiments (see above p, 89) the i^rre sting ac- 

 tion of a high degree of warmth seems to combine with the action 

 of air which is free from water vapor, AS regards the observa- 

 tion, thf^t abnormal cdll-divislon occurs in many fungi at high 

 temperatures, it seems to me that we are still Insufficiently 

 oriented as to the disarticulating action of temperature, 



g. Light 



The influence of light on the formation of tissue Is at any 

 rate slight, sine© no specific effects of this form of energy 

 are known. 



It was demonstrated that illuminati&n can cause the forma- 

 tion of chlorophyll and anthocyanln and that the formp.tion of 

 pigment is often lacking in the dark, But since it was shown 

 that the formation of chlorophyll (in various algae) is possible 

 even in the dark, when certain nutritive substances are added 

 and that, in the same way, cells can be incited to a formation 

 of anthocyanin independent of light or darkness,- we may assume 

 that the formation of pigment after illumination does not repre- 

 sent a very specific action of light, but that it is caused by 

 nutritive conditions, the production of which is raede possible 

 in the cells by the influence of the light. 



If the tissues in etiolated plants reach ©nly a moderate 

 degree of differentiation, while the individual cells often be- 

 come larger than under normal conditions, we may not see in this 

 any specific result of a lack of light, but the effect of saenty 

 nutrition and reduced transpiration. We observe the same tissue 

 changes in examples v/hich are raised in the light in a damp room 

 that we find in cultures made in the dark. 



The question as to v/hether continued illumination can 

 "arrest" certain formative processes, as seems to follow from 

 Bonnier's experiments (see above p, 5?), needs closer investiga- 

 tion. 



(278) 4, Chemical Substances 



So far as any insight into the factors v^hich are effective 

 in the formation of tissue is possible in the present state of 

 our knowledge, we may indeed maintain, that the great majority 

 of the processes of grovrth, formation and fiifferentiation are 

 brought about by stimuli given out by chemical substances. 



Witjiout doubt, each process of growth, etc. presupposes the 

 presence of certain substances, no matter whether they are sup- 

 plied to the cells from v/ithout or are produced in them autoch- 

 thonously by assimilation* If these substances core lacking, or 

 are present in insufficient amounts, certain processes of grov/th 

 and formation are omitted and "arrestment forms" are produced. 



