METAMORPHOSIS IN PLANTS. 95 



accumulated evidence is distinctly in favour of the material 

 view of metamorphosis ; that is, of a genetic relation be- 

 tween the various forms of any one member. To take 

 some simple illustrative cases : it is clear, for instance, that 

 a potato-tuber is produced by the actual metamorphosis of 

 an ordinary branch ; nor is it less clear that a turnip is the 

 product of the actual metamorphosis of an ordinary root. 

 The matter becomes more complicated, when we turn to the 

 leaves, on account of the great variety of form which these 

 members present, and calls therefore for more elaborate 

 treatment. For whereas in the cases of shoot and root 

 just mentioned, only a single metamorphosis takes place ; in 

 the case of the leaves, on the contrary, we have the question 

 of successive metamorphoses to consider, the transformation 

 of one metamorphosed leaf into another. 



In order to deal adequately with the metamorphosis of 

 leaves, it will be necessary for me to inflict upon you a brief 

 statement of the different classes or categories of leaves to 

 be met with on the plant, based on the classification pro- 

 posed by Alex. Braun l and by Hanstein. 2 They dis- 

 tinguish : — 



Belonging to the Vegetative Region. 



1. The Cotyledons, or seed-leaves, the first leaves of the 

 embryo plant. 



2. The Cataphylls, or scale-leaves, such as form the 

 covering of buds. 



3. The Euphylls, the ordinary green foliage-leaves. 



Belonging to the Reproductive Region. 



4. The Hypsophylls, including : — 



(a) The bracts, which are intermediate between the 

 foliage-leaves and the floral leaves ; (b) the 

 sepals, forming the calyx ; (c) the petals, forming 

 the corolla. 



1 Alex. Braun, " Yerjungung," Eng. Trans., p. 62. 



2 Hanstein, Bot. Abhandlungen, iv., 1882, p. 28. 



