ITS CHEMICO-PHYSICAL AND MORPHOLOGICAL PROPERTIES 31 



cellulose walls. The small cell spaces are completely filled up 

 with the cell-substance, which, with the exception of the nucleus 

 and chlorophyll, consists solely of finely granular protoplasm. 



Flemming recommends cartilage cells from young Salamander 

 larvas as affording the best and most reliable material for the 

 study of the structure of living proto- 

 plasm (Fig. 11). The cell-substance, 

 which during life, as in the young 

 plant-cells, completely fills the spaces 

 in the cartilaginous ground-substance, 

 is traversed by wavy threads of fairly 

 high refractive power ; these are less 

 than 1 jx in diameter, and are generally 

 most numerous, and at the same time FlG - "--Living cartilage cell 



. of a Salamander larva, much 



most wavy, in the neighbourhood of magnified, with distinctly marked 



the nucleus; sometimes the periphery threads. (After Flemming: from 

 of the cell is nearly, if not entirely, 



free from threads, but sometimes they are present in great num- 

 bers here also. 



2. Cells which contain several different substances in their 

 protoplasm. In plants, and in unicellular organisms, the pro- 

 toplasm frequently contains drops of fluid, in which salt, sugar, 

 and albuminates are dissolved (circulating substances). The 

 further we go (Fig. 12 A) from the growing-point of a plant, where 

 the minute elementary particles of pure protoplasm as described 

 above are grouped, the larger do the individual cells (c) appear, until 

 they are frequently seen to be more than a hundred times as large 

 as they were originally, whilst, in addition, their cellulose wall has 

 become considerably thicker. However, this growth depends only 

 to a very small extent upon any marked increase of the proto- 

 plasmic substance. The cavity of such a large plant cell is 

 never seen to be completely filled with granular protoplasmic 

 substance. The increase in the size of the cell is due much 

 more to the way in which the small amount of protoplasmic 

 substance, which was originally present at the growing point, 

 takes up fluid, which in the form of cell-sap separates out into 

 small spaces in the interior, called vacuoles. By this means a 

 frothy appearance is produced (Fig. 12 B, s). 



More or less thick protoplasmic strands stretch out from the 

 mass of protoplasm in which the nucleus is embedded. These 

 strands serve to separate the individual sap vacuoles from one 



