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 
Fig. 29. —Portion of inner epidermis of Onion bulb scale showing cells at 
various stages of maturity. Young cell (1); old cell (3); cell intermediate in age 
between 1 and 3 (2); cell wall (c); outer plasma membrane ( pi ); middle lamella 
(mO; nucleus (w 1 ); nucleolus (w 2 ); nuclear membrane (w 3 ),* cytoplasm (cy); 
vacuole (z/). Note that the young cell (1) 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 pedate. 
