THE GREEN LEAF 57 



CHAPTER VI 



THE GREEN LEAF 



WE now pass from the study of the lower 

 types of green plants to a consideration of the 

 higher and more specialised forms of terrestrial 

 vegetation. But if we restrict ourselves to 

 a comparison of the vegetative organs of the 

 more highly differentiated algae and of the 

 higher plants, we shall be struck, not so much 

 by the dissimilarities, as by the likenesses 

 which exist between them. We meet with 

 the same specialisation of the shoot into a 

 stem bearing thin expanded structures 

 the leaves. There are the same organs for 

 attaching the plant to rough surfaces, or 

 anchoring it in a looser sub-stratum. It is 

 not difficult to discern in the influence of light 

 the common factor which has been chiefly 

 concerned in the production of these resem- 

 blances, so far at least as external form is 

 concerned. 



But when we probe more deeply into the 

 matter the real differences between the two 

 classes of plants begin to make themselves 

 apparent. They consist, so far as the vegeta- 

 tive structure is concerned, in a specialisation 

 of cells on the part of the land plant which 

 may reach a grade of complexity almost 



