62 PLANT PHYSIOLOGY 



and even extreme, conditions, such as in cells that are growing, 

 reproducing, storing, synthesizing, resting, etc. Also the nature 

 of animal Protoplasm and its relations with that of Plants should 

 be included. 



Literature. The most important works for the student upon 

 this subject are Verworn's " General Physiology," and the summary in 

 Pfeffer's " Physiology," and in Jost's " Lectures." Valuable also, 

 especially for discussion of protoplasmic structure, is Wilson's " The 

 Cell in Development and Inheritance" (New York, Macmillan, 1904), 

 and there is an excellent summary article by him in Science, 10, 1899, 33. 

 On the emulsion structure of Protoplasm, upon its movement and the 

 imitation thereof by artificial microscopic foams, there is the important 

 work of Butschli, translated as " Protoplasm and Microscopic Foams " 

 (London, Black, 1894), of which descriptive reviews are in Science, 2, 

 1895, 893, and in Nature, 48, 1893, 594- Of fundamental importance 

 for protoplasmic movement is Ewart's fine monograph, " Protoplasmic 

 Streaming in Plants" (Oxford, Clarendon Press, 1903). But it is of 

 interest to note that the existence of the emulsion structure in living 

 plant cells has recently been denied by Degen in Botanische Zeitung, 

 63, i9°5> 2 ° 2 - 



SECTION 2. THE CHEMICAL COMPOSITION OF 

 PROTOPLASM. 



Protoplasm has been found to be, chemically, not a single 

 substance, but a mixture of many and diverse substances, includ- 

 ing some which are very complex and unstable. It is thereby 

 rendered very difficult for chemical study, to such a degree that 

 it is still doubtful whether there exists a distinctive chemical 

 Protoplasm to which the other constituents are secondary, or 

 whether it is simply a mixture without any distinctive life-con- 

 stituent. The practical chemical study of Protoplasm requires 

 methods and appliances so special as to make it a difficult phase 

 of organic chemistry, and it is not profitable for the student 

 to undertake such work as a part of this course. But he should 

 make himself acquainted through books with our present knowl- 

 edge of the chemical composition 0} Protoplasm, including the 

 composition 0} those important protoplasmic constituents, such as 

 nuclein and plastin, whose composition is known, the chemical 



