6 GENERAL DIFFERENTIATION OF THE PLANT-BODY 



with an essentially theoretical construction, as I have elsewhere explained l . 

 Goethe himself has plainly stated his view as follows : ' That which 

 according to our idea is equal, may in reality appear either as equal or as 

 similar, or indeed as completely unequal and dissimilar ; this is the essence 

 of the pliant life of nature.' In somewhat other form this idealistic notion 

 has been preserved, inasmuch as the history of development was raised by 

 the labours of K. F. Wolff, R. Brown, and Schleiden, to the rank of one 

 of the most important aids to organography. The view which I have 

 called the ' Differentiation theory ' is based, as indeed is the whole of the 

 doctrine of metamorphosis, on the study of the transformations of leaves, 

 the manifold character of which is well known. Had its foundation 

 been the transformation of the root instead of the leaf, the general notion 

 of metamorphosis as merely a hypothetical transformation would have 

 been replaced by the conception of it as an actual transformation a view 

 which, for many years, and in the face of active contradiction, I have 

 endeavoured to establish. The differentiation theory assumes that at the 

 vegetative point of the shoot indifferent primordia arise which are capable 

 of development according to the needs of the plant in manifold ways, 

 but have this in common they are ' leaves ' ; the other view assumes 

 a real transformation of a primordium in such a way, that, for example, 

 the primordium of a foliage-leaf, instead of developing actually into 

 a foliage-leaf, can become in the mature condition a leaf of quite 

 a different character, a scale-leaf, say, or a sporophyll ; similarly, the 

 primordium of a stamen might become a petal. It will be seen that 

 here a longer or shorter portion of the path of development is the 

 same in the two primordia, for instance, of a foliage-leaf and a scale- 

 leaf. We speak of the scale-leaf as a transformation of the foliage- 

 leaf, because in the juvenile condition w r e often find it to be possessed 

 of parts which unfold themselves in the foliage-leaf, but become arrested 

 in the scale-leaf; and further, we can experimentally hinder this trans- 

 formation. The point is so clear in a case such as this that I will 

 briefly illustrate it by an example 2 . Fig. i shows, at /, the outline of a 

 foliage-leaf of Acer platanoides, and at 77, the outline of a bud-scale. 

 The two are outwardly very different structures. The foliage-leaf consists 

 of the blade, L, of the stalk, 5, and of the very small leaf-base, G\ the 

 bud-scale shows no differentiation, nevertheless it is nothing else but the 

 transformed primordium of a foliage-leaf. If we examine more closely, 

 and under some magnification, the small black tip of the bud-scale we 

 find that it possesses a minute leaf-blade, or rather the rudiment of this, 



1 Vergleiehende Entwicklungsgeschichte der Pflanzenorgane. Schenk's Handbuch der Botanik iii. 

 i. p. 103. 



2 



See Goebel, Beitr. /.. Morphologic und Physiologic des Blattes, in Bolan. Zeitung, 1880, p. 753. 



