CHAPTER IX 



THE LAW OF PROENVIRONMENT 



It is a principle of general application for all organisms 

 that fixed or sedentary forms are less quickly responsive to 

 environal stimuli than are motile ones. So fixed Blue-green 

 Algse like Nostoc are less quickly responsive than free forms 

 like Oscillatoria; both of these are less responsive than a flagel- 

 late Bacillus, in which a special part of the protoplasm has 

 become modified and energized for locomotion. Plants again 

 as a group are greatly less responsive than most animals, since 

 they usually lead a fixed life. But that parts of their tissues 

 can become highly irritable is shown by the movements of 

 the leaf in Dioncea and Mimosa being more rapid and powerful 

 than the muscular movements of many animals. Plants 

 therefore, as a group, are greatly less specialized than animals, 

 though, when such a tissue as that of Dioncea becomes highly 

 sensitive, it exhibits many of the fundamental responses that 

 even the higher animals do. Continuity in stimulation action 

 and in response phenomena, is therefore unbroken from the 

 lower plant types up to the higher animals. The recognition 

 of this fact is of prime importance, when we attempt to learn 

 how all organisms have evolved. 



Many naturalists, in surveying the trend of evolutionary 

 advance, have recognized a principle or method of improve- 

 ment or of betterment as linking together the whole. Along- 

 side this, as indicated in the last chapter, may be an evidently 

 static state of the terebratuloid kind, in which neither progres- 

 sion nor degradation occurs. Not unfrequently however marked 

 degeneration or devolution can be observed; specially in sapro- 

 phytic and parasitic plants, and in sedentary or parasitic animals. 



But the first of these three stages has been the most attract- 

 ive phase of evolution, and so has received most attention. 



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