12 GENERAL DIFFERENTIATION OF THE PLANT-BODY 



We limit therefore the idea of transformation to cases where the 

 change of function is evident. Ike foliage-leaves in one and the same plant 

 frequently differ from one another in configuration, but where no other 

 functions than those of assimilation and transpiration appear prominent 

 it is better not to speak of a transformation but only of a different 

 construction. As is the case in all attempts to set artificial boundaries 

 in matters relating to living organisms, it is impossible here to draw 

 sharply defined limits, and especially between the small deviations in 

 function which always go hand in hand with differences in configuration. 

 In the root-system of a dicotyledonous plant, for example, the chief 

 root and lateral roots are organs which have essentially the same function 

 and configuration, and yet there are differences between the two of 

 physiological behaviour and of construction differences in which we may 

 recognize at one time phenomena of correlation, and at another dissimilarity 

 in reaction towards external influences. That a lateral rootlet owes the 

 differences which mark it from the chief root only to its position in the 

 root-system is apparent, inasmuch as it can be readily caused to develop 

 as a chief root. The differences between chief root and lateral root are 

 then too slight to allow of our speaking of a ' metamorphosis.' 



I have said above that if the doctrine of metamorphosis had been 

 developed upon the facts observed in the roots instead of the leaves it 

 would not have led to such illogical conceptions as has been the case. When 

 one speaks of a ' root ' in one of the higher plants one does not think of 

 it as an abstract idea but as quite a definite object a leafless cylindric 

 organ provided with a root- cap. This is so because in the root change 

 of function is a much more rare occurrence than it is in the ' leaf,' and 

 consequently it has not happened that the idea of the root has been 

 gradually generalized so as to leave only an abstraction with which nothing 

 can be identified. There are however not a few cases in which roots are 

 transformed, and these we can easily follow. For example, we see that the 

 root when it is transformed into a shoot throws off its root-cap, as in 

 Platycerium and some other ferns, as well as in some Spermaphyta ; and 

 the same thing happens, along with the necessary change in the tissues, 

 when the root becomes a thorn, as it does in Myrmecodia echinata and 

 Acanthorhiza aculeata, or forms a tuber to serve as a reservoir of food. 

 In the case of the root also, the change of function may set in before the 

 root has exercised its original function of a nourishing and anchoring 

 organ. 



The result of what has preceded is then as follows -.The idea that 

 morphology has nothing to do with the function of organs has been 

 acquired entirely because the fact has been overlooked that the trans- 

 formations seen in organs are conditioned by a change of function. 

 Their functions therefore have been treated as subordinate in determining 



