CHAPTER VI. 



MORPHOLOGICAL DIFFERENTIATION IN PLANTS. 



212. WHILE, in the course of their evolution, plants and 

 animals have displayed progressive integrations, there have 

 at the same time gone on progressive differentiations of the 

 resulting aggregates, both as wholes and in their parts. 

 These differentiations and the interpretations of them, form 

 the second class of morphological problems. 



We commence as before with plants. We have to con- 

 sider, first, the several kinds of modification in shape they 

 have undergone; and, second, the relations between these 

 kinds of modification and their factors. Let us glance at the 

 leading questions that have to be answered. 



213. Irrespective of their degrees of composition, plants 

 may, and do, become changed in their general forms. Are 

 their changes capable of being formulated? The inquiry 

 which meets us at the outset is does a plant's shape admit 

 of being expressed in any universal terms? terms that 

 remain the same for all genera, orders, and classes. 



After plants considered as wholes, have to be considered 

 their proximate components, which vary with their degrees 

 of composition, and in the highest plants are what we call 

 branches. Is there any law traceable among the contrasted 

 shapes of different branches in the same plant ? Do the rela- 

 tive developments of parts in the same branch conform to 

 any law? And are these laws, if they exist, allied with one 

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