VEGETABLE CYTOLOGY 



6l 



granular-looking. Within the cytoplasm will be observed a number 

 of clear spaces. These are vacuoles and because they are filled with 

 cell sap (water with nutrient substances in solution) are called "sap 

 vacuoles." 



Protoplasm is in intimate relation to water. The reaction of the 

 cytoplasm to a bounding film of water between it and the cell wall 

 forms the outer plasma membrane or ectoplasm, a clear homogeneous 

 outer band of cytoplasm; the reaction of cytoplasm to the water 



cpLnn rf cy 



mi' 



FIG. 29. Portion of inner epidermis of Onion bulb scale showing cells at 

 various stages of maturity. Young cell (i); old cell (3); cell intermediate in age 

 between I and 3 (2); cell wall (c); outer plasma membrane (pi)', middle lamella 

 (ml)\ nucleus (w 1 ); nucleolus (w 2 ); nuclear membrane (w 3 ); cytoplasm (cy); 

 vacuole (z;). Note that the young cell (i) shows numerous small vacuoles and 

 spheroidal nucleus near center of cytoplasm. In 2 (cell of intermediate age) the 

 cell has enlarged, larger vacuoles have formed thru the bursting of films of cyto- 

 plasm separating smaller ones, and the nucleus has moved toward the cell wall. 

 In 3, the films have all burst, the cytoplasm and nucleus have been pushed up 

 against the cell wall, the nucleus is flattened out, and a large vacuole appears in 

 the center of the cell. 



within the sap vacuoles forms the vacuolar membranes; the reaction 

 of the dense protoplasm of the nucleus to the water in the cytoplasm 

 around it forms the nuclear membrane. Upon mounting another 

 portion of epidermis in iodine solution, removing the excess of stain 

 and adding a drop of sulphuric acid and then examining under high 

 power, we note that the cell walls of cellulose are stained a deep blue. 

 A yellow line is evident in the middle of each cell wall and separates 

 each cell from its bounding cells. This line is the middle lamella 

 which is composed largely of calcium pectate. 



