ITS CHEMICO-PHYSICAL AND MORPHOLOGICAL PROPERTIES 33 



Fig. 13). Finally, in other cases, even these strands of protoplasm 

 in the interior of the cell may disappear. Then the protoplasmic 

 substance is represented solely by a thin skin, which lines the 

 interior of the little chamber, to use an expression of Sachs 

 (II. 33), as the paper covers the walls of a room, and which con- 

 tains one single large sap vacuole (Fig. 12 (7, left lower cell, and 

 Fig. 59). In very large cells this coating is sometimes so thin that, 

 except for the nucleus, the presence of protoplasm can hardly be 

 demonstrated at all in the cell, even when a high power of the 

 microscope is used, so that special methods of investigation are 

 necessary in order to render it visible. 



FIG. 13. A cell from a hair on a 

 staminal filament of Tradescantia 

 virginica ( x 240 : after Strasburger, 

 Practical Botany, Fig. 15). 



FIG. 14. (Edogonium, during process of form- 

 ing zoospores (after Sachs; from R. Hertwig's 

 Zoologie, Fig. 110): A a portion of the thread 

 of the alga, with the cell contents just escap- 

 ing ; C zoospore, which has reached the exterior ; 

 D stationary spore undergoing germination. 



It was by the study of such cells, that the earlier investigators, 

 such as Treviranus, Schleiden, and Schvvann, arrived at their 

 conception of the cell. Hence it is not surprising that they con- 

 sidered that the cell membrane and the nucleus constituted the 

 essential portions of the cell, and quite overlooked the importance 

 of the protoplasm. That this latter is the true living body in the 

 plant-cell too, and that it is able to exist independently of the 



D 



