174 BOARD OF AGRICULTURE. 



as a protection for the tender buds and fruit against the burn- 

 ing rays of the sun. 



About two centuries ago, the general structure of plants 

 was carefully studied and in many respects accurately de- 

 scribed by the celebrated anatomists, Grew and Malpighi, yet 

 having no knowledge of chemistry and but little of animal 

 physiology, they reasoned incorrectly concerning the functions 

 of the several parts. 



The earlier botanists very naturally regarded the root, the 

 stem and the leaf as the vital organs of the plant, and 

 ascribed to them certain functions. Thus Theophrastus said 

 the root was the stomach of the plant, designed to take up 

 nourishment, and Malpighi compared roots to hands, which in 

 the absence of the power of locomotion were extended for 

 food. Linnaeus also regarded them as the mouths through 

 which the plant was nourished. 



In like manner, the function assigned the stem was simply 

 to convey the food absorbed by the roots to the parts above 

 it and that of the leaf to exhale or perspire surplus moisture, 

 just like the skin of animals. After the discovery of the 

 atmospheric gases, about the beginning of the present century, 

 it was found that the leaf inhaled carbonic acid and exhaled 

 oxygen, which was regarded at first as a sort of respiration, 

 and this function was then added to that of perspiration. 



These half-truths of science concerning vegetables were 

 accepted as satisfactory for a time. It was found, however, 

 that a fraofment of a leaf or the cutting of a stem or a root 

 could readily be made to produce buds and perfect plants ; 

 that a plant might be inverted and its branches become roots, 

 while the former roots put forth leaves. Hence it became 

 evident that these were not true organs, with special func- 

 tions, like the lungs and stomach of animals, but were of 

 a complex nature, with various and, under some circum- 

 stances, interchano^eable offices. 



The earlier physiologists, like Perrault, Duhamel, Knight 

 and De Candolle, were impressed with the idea that some kind 

 of circulation was necessary for the distribution of nutriment 

 to the several parts of the plant, but they were unable to 

 devise any theory for the explanation of all the phenomena of 

 growth. There has been a prevalent idea, however, for more 



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