23 



Lecture 7, July 18, 1900. 



Light (contimied). 

 Water plants with regard to influence of light. 

 2 great types of leaves. 



1. Floating as water-lily. 



2 . Submerged . 



Leaves of water plants are in position to receive sufficient light. 

 Many water plants have two kinds of leaves, floating and suhmerged. 

 Ex. show that such plants can change the ]^X/^)i)( kind of leaf Txnder 

 different conditions. 



Proserpinaaoa very plastic, shows first dissected, then entir*?, 

 then dissected, then entire under different conditions. In water 

 plants other influences besides light seem to affect the leaves. 

 Finely-dissected leaves the type the general t2'"pe of submerged 

 leaves, since that form allows the light to sift through to a great 

 depth. 



Rosette plants . 



uot so common here. Dandelion, Serhm. This form cannot be 



explained by light relation ; yet, though plant as a whole avoids 



light, each leaf is so placed that it may receive some light. 



Tree rosette as tree fern, yuccas, palms, etc. Here leaves 



» 



seem to aorae under the same conditions as in the true rosette. 

 Comuouml leaves . 

 Compound and finely-divided leaves Kerner considers an 



