FUNDAMENTAL INTERNAL STRUCTURE OF PLANT BODY 7 



These spaces are called vacuoles. However, one must not 

 think of the cell-sap spaces in the protoplasm as vacuums, as 

 the rather inappropriate name "vacuole" may suggest. 

 Vacuoles are numerous and small in the young cells, but as 



Fig. I. — A, young cells from onion root tip; d., protoplasmic membrane; c, 

 cytoplasm; a, nuclear membrane; d, nucleolus; e, plastids (black dots). B, 

 older cells farther back from the root tip; /, vacuole; note that the cells have 

 enlarged. C, epidermal cell of Tradescantia zebrina; in its natural condition 

 of the right, and, on the left with the protoplast drawn from the cell wall as 

 the result of immersing the cell in a solution the concentration of which is 

 greater than that of the cell sap. . This phenomenon is called plasmolysis. g, 

 contains the plasmolyzing solution. (After Stevens.) 



the cell ages, they coalesce to form larger spaces. In some 

 instances, there is one large central vacuole, while the cyto- 

 plasm and nucleus are squeezed out close to the cell wall. 



