TISSUE FORMATION. 



59 



of vegetable products of this kind is very great. (Figs. 

 9 and 10.) 



FIG. 9. Cellular tissue of Cc- 

 reus variabilis, containing : a. a. 

 Jelly, b. Crystals, c. Starch- 

 granules. 



e / 



FIG. 10. a. b. Cells of a potato, containing 

 starch, c. Starch-grains apart, d. e.f. Wheat- 

 starch in different positions. 



10. There is often a deposit of silica on the cell-wall, 

 as in grasses, horsetails, and diatoms. Some of these 

 latter are beautifully marked with lines and dots, rival- 

 ing the most complicate patterns of engine-turned en- 

 graving. 



11. Cell-membrane, as all other kinds of formed mate- 

 rial, grows by addition inside, so that the inner layer is 

 the youngest. The formed material may get so thick 

 that nutrition ceases and the bioplasm is wholly trans- 

 formed, or dies. The solid deposit which fills up the 

 cells of woody fiber is known as sclerogen, or woody 

 tissue. (Fig. u.) In Coniferous plants the fibers are 



FIG. n. \Voody fiber. 



