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PART III. VEGETABLE PHYSIOLOGY. 



PART III. 



VEGETABLE PHYSIOLOGY. 



CHAPTER I. 



k 



Scope of Vegetable Physiology. — Properties of Protoplasm. 



Vegetable Physiology treats of the functions of plants, or, in 

 other words, of the way plants do their work, whether of vege- 

 tation or of reproduction. We have already touched upon this 

 subject. In Parts I and II, where we described the mechanism 

 of plants, we had, incidentally, more or less to say about the 

 functions of parts and of various processes that go on in the 

 plant. What was there said need not here be repeated, but it 

 remains still to be explained how the plant, as a whole, performs 

 its functions ; how it absorbs, digests and circulates its food ; 

 how, through the organs it possesses, it makes use of the chem- 

 ical and physical forces of nature to maintain its life, to build up 

 its tissues and to reproduce its species. 



All the activities which a plant exhibits are due to the won- 

 derful substance, protoplasm, the appearance and structure of 

 which have already been described. While the protoplasm lives 

 the plant goes on building up its tissues, appropriating constitu- 

 ents of the soil and air to repair its wastes, and exhibiting all the 

 profoundly interesting phenomena which belong to vegetable 

 life ; but when it dies, the intricate structure which it had built 

 up, and of which it formed a part, falls rapidly into ruins, and 

 the complex molecules constructed by its agency speedily decom- 

 pose into simpler forms, and ultimately return to the mineral 

 kingdom whence they came. 



The properties or attributes of protoplasm, that is, those 

 which serve to distinguish it from all those substances which we 

 call " dead matter," are, according to Dr. Michael Foster, six in 

 number, and may be stated as follows : 



