PHYSIOLOGY 41 



the physiologist. Finally, the ultimate result of all 

 the growth and reactions is the reproduction of the in- 

 dividual ; and the details of this culmination are also 

 within the province of physiology. 



Though the physiologist looks on the plant from quite 

 a different point of view from the anatomist, the mor- 

 phologist, or the cytologist, he must, nevertheless, 

 take into consideration the results of their work, for 

 there is no use in trying to make observations on the 

 work of a machine unless you know how it is put to- 

 gether, and what it is intended to do. The physiologist 

 must also have a considerable knowledge of organic 

 chemistry, for the processes that go on in the organs 

 of plants in the course of their breathing, feeding, &c., 

 are in reality complex chemical reactions, the key to 

 the comprehension of winch is a knowledge of the simpler 

 reactions which can be made to take place in test- 

 tubes and retorts. Indeed, a laboratory for the ad- 

 vanced study of plant physiology appears outwardly 

 very much like a chemical laboratory, with its glass 

 tubes and reagents and complicated pieces of apparatus. 



Speaking as a physiologist, the leaf is the most im- 

 portant part of a plant. The leaf is the actual factory 

 of the food of the world. In the leaf the carbon is ex- 

 tracted from the carbonic acid gas in the atmosphere, 

 and is worked up with the hydrogen and oxygen in 

 water to form soluble sugars, and is deposited tem- 

 porarily in the leaf as starch grains, which are carried 

 away as sugars and deposited ultimately in roots, 

 stem, or other places of storage. The atmospheric 

 carbon dioxide enters the leaf through the pores or 

 stomata in its epidermis, and the water which is in 

 every living cell is supplied from the soil by the roots. 

 The process of turning these simple elements into the 



