LIVING MATTER 



6i 



^^ci 



separating into two equal groups. Then a new wall is formed 



between the two new kernels. In the case of the ameba, 



the two halves of the 



naked protoplasm crawl 



away from each other 



and finally separate 



(Fig. 29). 



49. Tissues. In plants 

 and animals large 

 enough to be seen with- 

 out a microscope there 

 are usually many dif- 

 ferent kinds of cells. 

 ■Masses of similar cells 

 together make up a tis- 

 sue. In our own bodies 

 there are skin tissue, 

 muscle tissue, brain tis- 

 sue, bone tissue, gland 

 tissue, connective tis- 

 sue, and others. In the 

 body of an ordinary 

 plant we may recognize 

 bark cells, wood cells, 

 pith cells, skin cells, 

 and other tissue groups 

 (see Figs. 31, 32). 

 Each of the organs, 

 such as hand or eye, 

 flower or fruit, is made 

 up usually of several 

 kinds of tissue. The 

 hand, for example, has 

 in it every main class 



of tissue that is to be found in the human body. In the twig 

 of a tree we can find pith, wood, bark, epidermis, and so on. 



Fig. 32. Various kinds of plant cells 



1, epidermal, or skin, cells of a leaf, showing the 

 outer wall greatly thickened, and the cuticle; 



2, columnar cells, like those of the palisade layer 

 of a leaf pulp; 5, moving ciliated cells, like those 

 of typhoid bacilli; 4, swimming spores of a water 

 mold; 5, budding cells, like those of the yeast 

 plant; 6, guard cells inclosing a breathing hole, 

 or stomate, on the surface of a leaf; 7, a pollen 



tube growing out of a pollen grain 



