340 COSMIC PHILOSOPHY. [it. II 



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, accom- 

 panied 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, usually 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 glossy ; the cells composing 

 the lower stratum become less and less crowded, until the 

 result is a spongy surface, filled with innumerable pores, 

 through which the moisture of the plant may be exhaled. 

 Finally a differentiation arises between the axillary buds, 

 some of which elongate into branches, repeating the chief 

 characteristics of the stem, while others are developed under 

 the still more heterogeneous forms of flowers, with their 

 variously-cleft calyx and corolla, and their variously-com- 

 pounded stamens and pistils. 



In the fertilized mammalian ovum the earliest step toward 

 heterogeneity consists in the division and redivision of the 

 nucleated embryonic cell. As the cell-nucleus grows, by 

 continuous integration of the nutritious protoplasm in which 

 it is imbedded, it slowly becomes grooved, and ultimately 

 divides into a pair of nuclei, about each of which is formed 

 a cell-wall. This process continues until the entire yolk is 

 absorbed, by which time it has become differentiated into a 

 mulberry-like mass of cells. And these cells, at first all 

 alike spherical or nearly so, become club-shaped or hexagonal 

 or pointed, as the mass further consolidates and squeezes 

 them together. A grand differentiation next occurs between 



