210 PRACTICAL LESSONS IN SCIENCE. 



plants ; sometimes they are so formed as to serve as insect traps ; 

 sometimes they serve as storehouses for food and as foliage also, 

 and sometimes they appear as spines, tendrils or scales. Foliage 

 leaves are the most prominent parts of the plant, and are much 

 used in describing and classifying plants ; hence the necessity of 

 studying carefully the forms of leaves, and of naming them ac- 

 curately. Leaves differ in color. The under side differs from the 

 upper side. Sometimes they are smooth, sometimes hairy or 

 woolly, etc., all of which may be important details in the identi- 

 fication of a plant. To gather leaves, to study them in all their 

 details, to describe them accurately, is an interesting and valu- 

 able educational exercise. 



Leaves usually arise from definite places on the stem called 

 nodes or joints. If two arise from the same joint, they are on op- 

 posite sides of the stem, the pair above stand at right angles 

 with the first pair and the third pair above are directly over the 

 first, so that there are four ranks or rows of leaves along the 

 stem. Another arrangement is when the second leaf is opposite 

 but on the joint above, the third being over the first, when there 

 are only two rows of leaves along the stem. Another is when the 

 second leaf is on the joint above, but only one-third the way 

 around the stem, so that the fourth above stands over the first 

 and there are three rows of leaves along the stem. Sometimes 

 there are several leaves on one joint when they are called whorled 

 leaves, and sometimes, as in the pine, they form a cluster or fas- 

 cicle which appear to be the leaves of a whole branch, which is so 

 short that the leaves seem to arise from one joint, but examina- 

 tion shows a spiral arrangement. Other arrangements occur, 

 any of which can easily be made out from the careful study of 

 young stems. 



The buds from which branches grow are developed in the axils 

 of leaves, so that the branching of a plant or tree follows the 

 arrangement of the leaves and is always definite, although it is 

 often difficult to discover the law on the older parts of the stem 

 as many branches have been destroyed. This same arrangement 

 extends to the location of flowers on the stalk, so that while on 



