346 GENERAL SCIENCE 



We now see why plants and trees should be thinned out 

 sufficiently to permit them to get air and sunlight. 

 Plants that are crowding one another cannot be healthy 

 and productive. Fruit trees that are not properly pruned 

 and thinned have so many branches that they cannot all 

 get sunlight and sufficient air, and so the lower and inner 

 fruit-spurs or branches die and what little fruit is grown 

 is of inferior quality. Fruits like peaches and apples are 

 covered with openings for the inward and outward pas- 

 sage of gases, and for this reason they need sunlight and 

 air or they will not grow properly and will not be colored. 

 Even small twigs are covered with openings for the pas- 

 sage of gases; these openings can be seen with the unaided 

 eye and are called lenticels. 



Man and other animals are dependent upon the leaves 

 of plants for their food either directly or indirectly. 

 Hence man must learn how to care for the plants that 

 he wishes to cultivate in order to make them productive. 



237. Flowers. When a seed germinates, it first grows 

 a root, then stem, leaves, and finally at a comparatively 

 mature stage flowers appear. The flower is grown for 

 the purpose of producing new plants. To find how this 

 is done it is necessary to make a close study of complete 

 flowers. Examine some flowers of fruit trees, or wild 

 flowers from the woods, or some in the home, and find 

 all the parts. We shall see that some flowers contain 

 parts which are not necessary for reproduction and 

 some which are necessary for reproduction; the former 

 we call non-essential parts and the latter essential parts. 



The non-essential parts consist of the calyx and corolla. 

 The calyx is the outer whorl of leaf-like parts of the 

 flower and is often green in color. One of the divisions 

 of the calyx is called a sepal. The corolla is the second 



