TISSUES 77 



not as it appears in a picture, but as it exists in a plant, 

 one of millions working together and completing the life 

 of the plant. You will remember that this life is of 

 great importance to you. Just as your own life goes on 

 unceasingly in your body, you will think of the life of a 

 plant going on unceasingly in those millions of busy cells 

 which are hidden within it. It is a life which words and 

 pictures and microscopes cannot portray. They can only 

 reveal certain dead evidences of it. The thing itself you 

 must imagine. The cells are the seat of real life like your 

 own. You must examine them dead, but you must think 

 of them alive. 



24. Tissues. — A tissue is a group of similar cells. 

 There are scores of different kinds. Epidermis is the name 

 of one. It is the tissue which is on the outside. Wood 

 and pith are other kinds. The milk of the milkweed stem 

 is contained in the cells of a certain tissue which manu- 

 factures it. When this tissue is cut, the milk flows as 

 blood flows from a cut blood vessel. ' There is one tissue 

 through which the water absorbed by the roots ascends to 

 the leaves, another by which the food manufactured in the 

 leaves goes to other parts of the plant. There are tissues 

 which strengthen, like the tissue which strengthens the 

 wheat stalk. There are tissues which protect, like the 

 outer tissues of buds. There are tissues in which food is 

 stored, as in the potato. There are tissues in which food 

 is made, and these tissues are green, as in leaves. Thus 

 the plant body has its work subdivided, but all the tissues 

 cooperate, each making some contribution to the two great 

 ends of nutrition and reproduction. 



The pictures (see Figures 24, 29, 30) show the appearance 



