4 GROWTH AND WORK OF PLANTS 



often drawn out into strands, the clear spaces becoming larger 

 and the strands connected with a layer of protoplasm which lies 

 next the wall. The clear spaces are vacuoles and are filled with 

 cell sap. Somewhere in the protoplasm of the cell there is a 

 denser body, the nucleus of the cell. The nucleus is part of the 

 living substance of the cell, but is a distinct organ* of the cell. 



Fig. 3- 



Cells from a stamen hair of spiderwort (Tradescantia). At left, a young cell with small 

 vacuoles; at right, a mature cell with large vacuoles showing strands of protoplasm, and cur- 

 rents of protoplasm flowing as indicated by the arrows around the nucleus, through the strands 

 and in the wall layer of protoplasm (circulation). N, nucleus (a small nucleolus within); 

 Pr, protoplasm; V, vacuole; C. W '., cell wall (highly magnified with a microscope). 



6. Properties of protoplasm. Protoplasm possesses certain 

 properties which are peculiar to it. Its most wonderful property 

 is that of life. It is the living substance of all organisms. This 

 property of life man has not yet been able to explain. Some of 

 the other properties are as follows: i. Movement, under certain 

 conditions it is capable of motion, a streaming movement (circu- 

 lation) along the strands or in different parts of the cell, or a 

 rotation (cyclosis) around the cell next the cell wall (as in Elodea, 

 Nitella, etc., see fig. 200) ; 2. irritability, it is sensitive to heat, cold, 

 touch, electricity, etc.; 3. assimilation and growth, it can assimi- 

 late certain substances, resulting in the building up and increase 

 of the protoplasm; 4. reproduction, the unit of protoplasm with 

 its nucleus (the cell, or protoplast) is capable of reproduction, 

 i.e., of multiplication, or the formation of new units or cells. 

 (This takes place by division of one into two, then two into four, 



* In the older use of the term protoplasm the nucleus was believed to be only 

 a denser part of the protoplasm. Now it is known to be a distinct organ, and 

 the term cytoplasm is applied to the remaining part of the protoplasm. See 

 paragraph 364. There are other living bodies in the cells of many plants, 

 as well as organic bodies which are not living, but this is not the proper place 

 to describe them. 



