52 LEAVES 



supply for the cattle may be very limited. Every good farmer 

 knows the advantage of using sheep or goats for the cleaning 

 of neglected lands of these armed weed pests which most live- 

 stock will not touch. 



Leaves also serve for the storage of food and water as in 

 the case of the so-called " century plant," which grows for a 

 number of years and then develops its flowers and seeds at the 

 expense of the food stored in the large fleshy leaves. This is 

 no more wonderful than the common cabbage in which exactly 

 the same thing occurs in a cycle of two years; the accumula- 

 tion of the food is during the first, and producing the flower 

 and seed during the second year. Man has taken advantage of 

 this tendency of the plant to store its food in the leaves and 

 makes use of many such plants as food for himself. Leaves may 

 also serve for the storage of air as in the case of the floating- 

 plants which contain large air-chambers. 



In some few plants the leaves have undergone modifications, 

 enabling them to serve as insect traps for the capture of insects 

 which die, decay, and furnish a supply of nitrogenous food for 

 the growing plant. The most interesting insect catchers are the 

 sun-dew, Venus fly-trap, and the pitcher plants, which you 

 will find described in an encyclopedia, and in many works on 

 botany. 



Probably the most important function of leaves after photo- 

 synthesis is the formation of flowers and fruits, for as we shall 

 learn later, the flowers are modified leaves. (Page 54.) 



EXERCISES 



1. Collect the following forms of leaves: simple net-veined, simple par- 

 allel-veined, simple palmate-veined, compound palmate-veined and com- 

 pound pinnate-veined. Make drawings and label the parts. 



2. Collect and make drawings of leaves with and without petioles. 



3. Collect leaves showing different types of stipules. 



