24 



LIVING MATTER OR PROTOPLASM. 



Structure. Protoplasm differs slightly in appearance in differ- 

 ent plants and animals, and in different parts, and different stages 



FIG. 12. (After Sachs.) Young growing cells from the extreme tip of a stonewort (CTiara): 

 , membrane; i, nuclei; p, protoplasm; r, vacuole filled with sao. ( x 550i. 



of development, of the same individual. The protoplasm of very 

 young structures is considered to be the simplest or most typical, 



as it appears, for instance, in the eggs 

 of many animals, or in the cells of very 

 young vegetal shoots. Such protoplasm 

 is called typical or unmodified. As it 

 grows older it usually changes more or 

 less, both in chemical and physical prop- 

 erties, and in appearance. In the cells of 

 a young organ (Figs. 1 and 12), proto- 

 plasm is a transparent, semi-fluid or viscid, 

 granular substance which has a watery 

 appearance but shows no tendency to 

 mix with water. Treated with solu- 

 tions of certain coloring matters (for 

 instance. with iodine) it generally ab- 

 sorbs them from the solution and be- 

 comes deeply colored, often assuming a much darker shade 

 than that of the solution. Under moderately high powers of 





FIG. 13. (After Ranvier.) 

 Part of a single fibre of vol- 

 untary muscle from the leg 

 of a rabbit, p, protoplasm ; 

 n, nucleus. ( x 700). 



