COSMIC PHILOSOPHY 



Then while the bark gradually becomes differ- 

 entiated into the liber, made up of woody tissue, 

 tne a g reen an d corky envelopes, made up of 

 parenchyma, and the epidermis, the interior be- 

 comes differentiated into the pith, the medullary 

 sheath, the woody layer, made up of bundles of 

 greatly elongated cells, and the medullary rays, 

 or what is called the silver grain in maple and 

 oak. Meanwhile, between this heterogeneous 

 bark and the heterogenous wood which it sur- 

 rounds, there appears a zone of delicate cells, 

 charged with dextrine and other assimilable mat- 

 ter, and known as the cambium layer. At the 

 same time differentiations are going on at the 

 upper extremity of this complicated structure. 

 Portions of the green envelope protrude from 

 between the liber and the epidermis, accompa- 

 nied by tough fibres sent forth partly by the liber 

 and partly by the woody layer. While the green 

 portions flatten out horizontally, the fibres ramify 

 through them and serve to stiffen them ; and thus 

 is developed the leaf, which, when mature, usu- 

 ally exhibits a further differentiation between 

 blade and petiole, while by a continuance of the 

 same process stipules often appear at the base 

 of the petiole. Nor is this the end of the story. 

 For while the chlorophyll-cells that make up the 

 upper stratum of the leaf-tissue remain densely 

 crowded, and are often covered by a wax-like 

 cuticle, making the upper surface smooth and 

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