MODIFICATION OF THE ORGANS OF PLANTS 73 



is only the case with the basilar leaves, which sur- 

 round the winter buds. 



The modifications of the basilar and apical leaves 

 of Serratula centauroides are similar to those of Eosa 

 rugosa, and it is therefore unnecessary to repeat the 

 description. 



Those of the apical leaves tend towards their 

 protection from rain. When rain falls upon the 

 radical leaves, they are flattened out upon the 

 ground, which prevents them from being torn. 

 This is not so with the apical leaves, and had 

 their primitive structure remained unchanged, they 

 would have been constantly exposed to destruction. 

 M. Stahl 1 has shown how these leaves have pro- 

 tected themselves by shortening their petioles and 

 fringing their edges. In this way the leaf has 

 acquired greater resistance, and the water is better 

 enabled to run off it. This modification, however, 

 although one advantageous to the plant, has in- 

 volved the partial degeneration of the petiole and 

 the blade. 2 



3. Sagittaria Sagittifolia. The Sagittaria is an 



1 E. Stahl, Regenfall und Blattgestcdt (Ann. du Jard. hot. de 

 Buitenzorg, vol. xi., 1893). 



2 In the leaves (fig. 39, B and c), immediately above the foliage 

 leaves, the petiole gradually disappears altogether, while the blade 

 has become deeply serrated, thus providing for the water drainage 

 while retaining an assimilative surface. 



Further up the stem the leaf blades are more and more reduced, 

 until eventually they are no longer differentiated into hypopod and 

 epipod, but arise directly from the growth of the primordial leaf 

 (fig. 39, D to F). 



