MORPHOLOGY OF HIGHER PLANTS. i8i 



aration of crystals, as in Hydrastis (Fig. 292). 7. Blue with dilute 

 iodine solution, except the dextrin starches, as in mace, which are 

 colored red. 8. Sphere-crystalloids in fresh material treated 

 with alcohol. 9. (See page 167.) 10. Colored blue with alco- 

 holic solutions of methylene blue. 11. Reddish-brown with cop- 

 per acetate solutions. 12. Green with copper acetate solutions. 

 13. Separation in the form of large globules on the application 

 of sulphuric acid or solution of chloral hydrate. The essential 

 oils are more soluble in alcohol than the fixed oils, which are 

 usually only completely removed from the cells by the use of 

 ether or a similar solvent. 



THE CELL WALL. 



Origin and Composition. — The cell wall is formed by the 

 protoplasm, and varies in composition at different stages of the 

 growth of the cell, and according to the various functions it has 

 to perform. 



In order to thoroughly tmderstand the nature and composi- 

 tion of the cell wall, it is necessary to study the origin and forma- 

 tion of new cells. Growth of the plant is attended not only by 

 an increase in the size of the cells, but by the division of these 

 new cells are also formed. Cells that have the property to divide 

 and form new cells are known as meristematic cells and constitute 

 the MERiSTEM. The new and dividing walls resulting from the 

 division of the cells consist of a number of substances. When a 

 cell divides the two daughter protoplasts which result from the 

 division of the nucleus and cytoplasm are separated by the forma- 

 tion of a new wall between them (Fig. 94, 10). The first layer 

 formed is apparently different from the subsequent layers and is 

 known as the middle plate or middle lamella. This layer is 

 soluble in, or readily attacked by, solutions of the alkalies or solu- 

 tions containing free chlorine. It is insoluble in sulphuric acid, 

 and readily stained by the aniline dyes. While usually more or 

 less permanent, this middle plate may be finally absorbed, as in 

 the secreting hairs of kamala, or it may be changed into mucilage, 

 as in chondrus, or transformed into pectin compounds, as in fleshy 

 roots and fruits. 



