54 PLANT-LIFE ON LAND [CH. 



makes it possible to compare the regions of the plants 

 in which those organs occur ; that is, to compare the 

 flower of the higher plants with the fertile region of 

 Ferns or Club-Mosses. It is upon such comparisons 

 that it will be found possible to base an opinion as 

 to the true relation of the flower to the foliage region, 

 and to understand the underlying similarity of con- 

 struction which they show. 



The obvious analogies which exist between the 

 flower and the foliage-shoot in the higher plants did 

 not fail to attract the attention of some of the early 

 observers. Wolff, in his Teoria generationis, published 

 in 1759, wrote that " In the whole plant whose parts 

 we wonder at as being at the first glance so extra- 

 ordinarily diverse, I finally perceive after mature 

 consideration and recognise nothing beyond stem 

 and leaves.... Consequently all the parts of the plant 

 except the stem are modified leaves." Not many 

 years later the poet Goethe elaborated this general 

 conclusion into the theory of "Metamorphosis," which 

 is associated with his name. He recognised as 

 Metamorphosis the process by which one and the 

 same organ, for instance the leaf, presents itself to 

 us in various modifications, such as the foliage leaf, 

 sepal, petal, or stamen. He then went on to 

 distinguish as examples of "progressive metamor- 

 phosis" those changes of type of the appendages 

 which proceed from the cotyledons or seed-leaves 



