Functions of Leaves 85 



stipules, embraces the stem, the leaf is amplexicaul, the part 

 surrounding the stem being called the vagina or sheath. 



If the stem grows through the leaf, the latter is said to be 

 perfoliate (fig. 141), whilst, if any part of the leaf adheres to 

 the stem, causing the latter to be winged (fig. 142), the leaf is 

 said to be decurrent. 



Fig. 142. — Decurrent leaf of Syinphytum offi- 

 FiG. 141. — Perfoliate leaf of cinale^ the stem hence becoming winged on 



Bupleuntm rotundifoHuTn. one side. 



If the leaves grow from the point of junction of the root 

 and stem, or if the stem be so reduced as to be almost obli- 

 terated, they are said to be radical. Leaves growing from the 

 main stem are called cauline, and those from the branches, 

 ramal. 



FUNCTIONS OF THE LEAVES. 



I. To absorb food for the plant. — We have already seen 

 how the roots take up from the soil the various substances 

 needed for the life of the plant. One very important substance, 

 however, is not taken up by the roots of green plants, and this 

 is carbon. 



Thife element exists in the atmosphere in the form of carbon 

 dioxide or carbonic acid gas, a compound of carbon and 



