A« Ooncerninff the Active gaotora 232 



All abnormal procespee of grov/th aitd formation in plants 

 are •bvlously cQused by definite external life-conditiorsB , In 

 the present section we will attempt to mention by name those 

 factors v/hich become influential in the formation of plcint tia- 

 sues and can cause the production of abnormal forms,- and also 

 to study the way they act. The science t© v/hloh we will en- 

 deavor to furnish some contributions by considerations of this 

 (ET4) kind, has been called, since Rou3c, the developmental me ohanioa 

 of orga ni sms . 



We will encounter many difficulties when busted with ^l^i^ 

 task,- so that it is aftvisable to become closely acquainted with 

 them from the beginning. 



In the "introduction" mention was made of the fact that the 

 investigator who works experimentally, will find himself, in a 

 favorable position for the "study" abnormal ]>lant tissues, sinte 

 it is now possible to produce artificially and at will most of 

 the forms of abnormp-1 plant tissues, We will not deceive our- 

 selves, however, with the thought thct we can experimentally 

 cause definite processes to take plaod xTlthout having some know- 

 ledge of the factors actually at work:- Even v/hen we have recog- 

 nized definite factors as participants in the production of any 

 processes, it is especially difficult to ascertain the specific 

 action of each of these factors separately and to distinguish 

 it from that of the other active factors. 



Callus tissues furnish s goed example of this, As is well- 

 knov/n, they are produced "after injury". But in this, nothing 

 has been said about the active factors. Obviously, at the time 

 of injury, definite cells and tissues are freed from the pres- 

 sure of their turgid neighbors. Therefore, the conditions of 

 strain and pressure are changed by the injury. If plants aftd 

 plant organs are involved, v;hich are not covered with water, the 

 I>art of the plant exposed will undoubtedly lose more water thru 

 transpiration after the injury than before it. The asmotic 

 pressure in the exposed cells and tissues v;ill be changed, the 

 diosmotic exchange of substances from cell to cell being Influ-' 

 enced thereby. Further, in the cells at the edge of the Injury, 

 the cytoplasmic fragments and the products of de opposition from 

 the destreyed, dead adjacent elements will exert chemical ac- 

 tions, while contact with the new medium,- air or v;ater - v/ill 

 have an unusual influence on the eJtp&Sed cells. It should be 

 recalled, from the earlier discusiifen, that each of the factors 

 hfere named can also have great influence on the tissue formation 

 of the plants. Therefore, it seems very possible that they are 

 also significant in" the formation of callus tissiacs. How shall 

 we isolate, however, the different factors from one another, in 

 the case of injury to the object unde» experimentation and as- 

 certain their specific method of effect in the comparative ex- 

 periments? Our xaresent methods do not always maSe it possible 

 to oarry through this isolation experimentally. Besides, even 

 with the methods now at our disposal, there still remains much 

 tc be investigated. At present v/e do not know what is the sig- 

 nificance of the above enumerated factors in the formation of 

 callus, nor whetlwr perhaps the essential ones are still unnamed. 



The conditions in many galls are even more complicated. 

 Many of those vrhioh we have termed prosoplasmas have been pro- 



