CELL STRUCTURE AND PROTOPLASM 23 



living contents. The cell wall, indicated by the border line, 

 is a non-living secretion of the protoplasm, most of which is 

 cellulose, a substance similar to starch in its composition. 

 This stretches as the cell increases in size, and becomes thick- 

 ened with the age of the cell by addition from the proto- 

 plasm. Recent studies have shown the wall to be made of 

 an extremely fine network of needle-like crystals. Most 

 important is the strength and shape the cell walls give to a 

 plant. The main portion of the cell, the protoplasm, is the 

 living, nearly transparent material which may be further 

 divided into cytoplasm and a spherical more dense portion 

 with a net-like structure, the nucleus. The protoplasm is a 

 complicated chemical compound made up of carbohydrates, 

 proteins, water, fatty substances, and simple compounds 

 of mineral salts so organized as to have the characteristics 

 of life. The synthesis of the protoplasm is an important 

 function of growth similar in all organisms, so far as is 

 known at present. Next to water, protein is the most abun- 

 dant, most variable, and therefore most studied constituent 

 of protoplasm. In addition to the elements carbon, hydro- 

 gen, and oxygen, found in carbohydrates and fats, proteins 

 have nitrogen and sulphur, and usually other mineral ele- 

 ments in very small amounts. The non-living often invisi- 

 ble content of the cell, scattered through the protoplasm, is 

 made up largely of solutions of salts, sugars and other food 

 materials. This non-living food matter is usually either in 

 one or more spaces, called vacuoles, near the center of the cell 

 or in many vacuoles scattered throughout the protoplasm. 

 The above is shown in outline form with additional sub- 

 divisions. 



daughter chromosomes away from the equator of the spindle. 7, 8, 9, Telophase. In 7, 

 daughter chromosomes form two compact masses. 8, Reorganization of resting nuclei 

 begun, the double nuclear threads become apparent, nuclear membrane and nucleolus 

 appear. In 9 the nuclear net is forming and the new cell wall separates the two new 

 cells. (Reprinted by permission from Holman and Robbins' Textbook of General 

 Botany, 4th edition, John Wiley and Sons, Inc., 1938.) 



