CHAPTER IX 



LEAVES 



General Facts in regard to the Life of Leaves — Experiments, rough 

 and exact — Stimmary of Leaf Ftmctions — The Structure of 

 the Leaf — Palisade Cells and Chlorophyll Grains — Shapes of 

 Leaves — Leaves adapted to special Functions — Substitutes for 

 Leaves — Vitality of the Leaf- — Fall of the Leaf. 



General Facts in regard to the Life of Leaves. 



— The leaf is the most distinctive part of the plant. There 

 are many rootless plants, such as the bladderwort which we 

 have already described ; there are many plants without 

 stems, such as the seaweeds ; but few plants can be called 

 leafless. Where the leaves are suppressed the stem is 

 modified to take their place. 



The leaf may be also viewed as the primitive part of the 

 plant. For among the seaweeds there is nothing but leaf, 

 there are no true stems nor roots. The liverworts, which 

 spread over the damp banks of streams, are still mostly leaf, 

 provided, however, v/ith suctorial rootlets on their under 

 surfaces. With the mosses and the ferns stems begin. 



It is therefore natural to suppose that the leaf is the 

 most essential part of the plant so far as the sustenance of 

 life is concerned. We shall see how true this is. Let us 

 think over the familiar facts in regard to the life of plants 

 which may give us hints as to the nature of the leaf 



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