THEORY OF VEGETATION. 



17 



Leaves are composed of footstalks, and the blade 

 or body of the leaf. The footstalk of the leaf is 

 formed by the vessels of the medullary canal. 

 These vessels ramify in the tissue, and form the 

 channels of the sap. The body of the leaf is 

 formed of cellular tissue covered with a thin skin 

 or epidermis, which is pierced with innumerable 

 apertures called stomata. In fact, these stomata 

 or mouths are to be found on all growing portions 

 of vegetables, not only on the leaves, as before 

 stated, but also on the shoots themselves, and on 

 the fruit. Their functions are very important in 

 vegetable life, as will be explained presently. 



Flowers are composed of floral envelopes and 

 of sexual organs. The floral envelopes are the 

 calyx and the corolla. The divisions of the calyx 

 are known as sepals, and those of the corolla as 

 petals. The sexual organs are the stamens and 

 the pistil. The stamens are the male organs of 

 plants. The anther, at the extremity of the stamen, 

 contains the pollen or fertilising dust. The pistil 

 is the female organ of plants, the extremity of 

 w T hich is called the stigma, and the base the ovary, 

 while the intermediate space is called the style. 



The fruit is composed of the pericarp, a fleshy 

 substance which is formed of cellular tissue, and 

 of the seeds. The seed contains the rudiment of 

 a similar plant. 



B 



