40 



A TEXTBOOK OF BOTANY 



[Ch. Ill, 5 



in an unbroken protoplasmic succession to the very first 

 living organism of the earth. As to the source of the pro- 

 toplasm of that first being we know nothing, though we 

 have two hypotheses, both of which may be groundless. 

 One relies upon an original case of spontaneous genera- 

 tion, even though perhaps never repeated. The other makes 



protoplasm itself an evolu- 



fe / 





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i-.*:. .:■ oT.'y .>'•;,■ '-^i ,--$■■$>■ 



tion from earlier and simpler 

 substances, suited to the dif- 

 ferent earlier conditions of 

 the earth, and thus carries it 

 back to an origin contempo- 

 raneous and equi-causal with 

 the origin of non-living mat- 

 ter. The former is rather the 

 mechanistic, and the latter 

 the vitalistic view of the 

 subject. 



There remains one very 

 important characteristic of 

 protoplasm, and that is its 

 organization within the indi- 

 vidual plant or animal. In 

 most organisms the proto- 

 plasm is subdivided into the 

 microscopically small masses 

 constituting the cells. This 

 subdivision, however, is not complete, for suitable methods 

 always show that through the cell walls run protoplasmic 

 threads, which, though extremely fine, suffice to keep the 

 different cells in physiological continuity (Fig. 15); and such 

 threads seem to unite all of the living cells of a plant into 

 one protoplasmic system. 



Within each cell the protoplasm shows a definite organi- 

 zation, clearly exhibited in typical form in our Figure 12, and 

 represented in principle in our generalized picture, Figure 16. 



Fig. 15. — A typical example, in 

 Mistletoe, of the continuity of proto- 

 plasm by threads through the cell 

 walls. The walls have been made to 

 swell in order to render the threads 

 more clearly visible. (From Stras- 

 burger, Jost, Schenck, and Karsten, 

 Text-book.) 



