SIGNIFICANCE OF MALFORMATIONS 179 



become normal and serves the purpose of propagation, as is the case 

 in Poa alpina and Poa bulbosa. 



These examples will suffice to show that it is impossible to frame 

 a generally applicable definition of the notion of ' malformation.' As 

 I have said, those malformations can be best characterized in which con- 

 spicuous changes of the organs have taken place. We find also, if we 

 disregard cases of chorisis, concrescence, and pleiomery, that there is very 

 commonly a change of function, which may go so far as to annul com- 

 pletely the normal function, and with this a change of configuration is 

 associated. Stamens become petals or carpels, or structures which are 

 partly carpels and partly stamens. These transformations have naturally 

 a special interest in relation to the doctrine of metamorphosis. 



I. 



SIGNIFICANCE OF MALFORMATIONS IN ORGANOGRAPHY. 



Whilst we find malformations of any morphological part, the trans- 

 formations they effect are yet not without rule a leaf, for example, is 

 never transformed into a shoot or into a root, nor does the converse 

 take place l . This is a point of some importance because it shows us 

 that once an organ has been laid down its development is bounded by 

 definite limits 2 . The papilla which develops into a lateral shoot has 

 often the external appearance of the primordium of a leaf; but they 

 must be intrinsically different. Were it otherwise we could not under- 

 stand why amidst the fundamental disturbances which are observed in 

 many malformations of flowers a transformation of one into the other 

 does not take place. As a matter of fact it was concluded at a very 

 early period from a study of malformations of this kind that petals, 

 stamens, and carpels, are ; leaves,' greatly though they often differ from 

 foliage-leaves in their external configuration. When we know the normal 

 history of development of a plant-organ we can often recognize even 

 in the mature condition the stage of development at which the divergence 

 from the normal in a malformation began, and it is a fundamental principle 

 that a malformation can only be understood through knowledge of the 

 normal development. 



Disturbance of the normal development in the sporophylls of the 

 flower, the stamens and carpels, becomes visible in an arrest of the 

 sporangia, the pollen-sacs and ovules, and frequently these do not 



1 Although in the normal formation of organs of Utricularia the limitation between shoot and 

 leaf entirely disappears. 



2 See page 8. 



N 3 



