224 



reaction to stimulus observed in the cells, numerous different 

 transitional stages can be made possible. One or more of 

 these transitional stages can represent reactions to stimuli 

 on preceding ones, others can not be understood as due to stim- 

 ulus effect (in the above «iv«cussed sense), but as the effect 

 of the force of the energy supplied. The detailed knowledge 

 of these "chains of stimuli", whose end links in these cases 

 represent processes of growths or formation, is still absolutely 

 closed to us;- in only a few cages are we at present in a posi- 

 tion to name a few links of the problematic chain of stimuli ^ 

 and to make probable any causal connection, The numerous works 

 whose authors have taken up experimentally the questions of 

 pathological plant anatomy, often throw much light on the ques- 

 tion as to how plants can be brought to a production of these 

 or those tissue forms. But any further dissection of the active 

 factors and the course of their action has been attempted only 

 in exceptional cases and not always successfully. 



If v7e find in an experiment that similar formations of 

 tissue are produced through the action of unlike factors, from 

 v7hat has been said already, we will have to make tests as to 

 whether possibly a dissimilarity of the effective factors has 

 only seemed to exist here, because of our scanty knor, ledge of 

 the so-called "chain of stimulation", or whether, by more exact 

 proof, similar effects and reactions majr not become tra-oeable 

 back to similar causes. Only when a positive answer to this 

 question has been proved impossible, will we admit the suppos- 

 ition, that stimuli of different kinds can bring about similar 

 formation reactions. 



When plants cultivated in the dark display tissue hypo- 

 plasia, as do those examples which are matured under water or 

 in a scarcity of carbon dioxide, we do not venture to find in 

 this a specific action of scarcity of light or of contact with 

 water etc., but must look for the cause of the hjrpoplasia In 

 the tertiura comparationis, in insufficient nutrition, to the 

 results of v^hich, the non-assimilating and weakly or non-trans- 

 piring plants are equally exposed. If fluctuations in temper- 

 ature and changes in the concentration of the surrounding 

 medium cause the same abnormal processes of growth, we do not 

 find in them any specific action of the temperature or the 

 Solution as then present, but must think of the fluctuations of 

 turgor and of osmotic pressure, caused by the changes in tem- 

 perature and concentration^ we must seek in them the cause of 

 the described processes of growth. If the same tissues are 

 formed after the mutilation of parts of plants, as gfter the 

 infection by fungimetc, the question confronts us as to wte ther 

 there may not exist factors,- causally conditioned by injury- 

 or infection,- which in this case as in that become effective 

 and cause in both, apparently dissimilar, cases the known re- 

 actions on the part of the organism. Since our scant knowledge 

 of the effective methods of external factors and the capacity 

 for reaction of cells and tissues for the present makes possi- 

 ble the giving of any satisfactory answer only in a few cases 

 naturally nothing can be said against the justification in 

 principle of my interrogation. 



(275) Since we tract certain kinds of arrestment formations back 

 to insufficient nutrition and recognize in the fluctuations of 

 osmotic pressure the cause of certain abnormal phenomena of 

 growth and the like, we thus become acquainted with specific 



