STRUCTURE AND PROPERTIES OF PROTOPLASM 75 



Literature. On this subject there is an immense literature, 

 especially on Irritability; it will be considered later under that sub- 

 ject, and here we need only note the most general papers, which, in 

 addition to the works of Pfeffer, Jost, and Verworn, are the follow- 

 ing. On streaming of Protoplasm there is the admirable monograph 

 by Ewart, " Protoplasmic Streaming in Plants " (Oxford, Clarendon 

 Press, 1903), which brings the subject so nearly to the present date 

 that I have since noted only a single paper of importance, Schroter 

 on streaming in moulds in Flora, 95, Erganzungsband, 1905, 1. An 

 older paper which will repay study is Velten's in Flora, 34, 1876. 

 An admirable summary of all the literature upon the general subject 

 of the effects of external conditions upon Protoplasm is in Part I of 

 Davenport's " Experimental Morphology." 



SECTION 5, THE BUILDING OF ORGANISMS BY 

 PROTOPLASM. 



In these studies so far Protoplasm has been studied simply 

 as a unit without regard to any organization it may exhibit. 

 Its masses, however, are not formless, but are highly differentiated 

 in structure, presumably in correlation with function. The 

 subject is one for study by the anatomist, histologist, and cytolo- 

 gist, as well as by the physiologist, but its physiological impor- 

 tance here demands some unified consideration which, neces- 

 sarily, must be rather theoretical than practical. For complete- 

 ness of the subject, and as a basis for future studies, the student 

 should inform himself upon the state of knowledge of its 

 important phases, which are included under the following 

 headings : 



(a) The differentiation of Protoplasm into specialized struc- 

 tures, cytoplasm, nucleus, plastids, with vacuoles and wall; the 

 known or supposed significance of the division and functions 

 of the parts, {b) The division into protoplasts or cells, and its 

 meaning; sizes of the cells and the determinants; method of the 

 division and its meaning, (c) Construction of the skeleton; 

 the cell wall and its substance, with the composition of the latter 

 and its derivatives; the diverse cell shapes and their meanings. 

 (d) The physiological continuity of the different protoplasts 



