BOTANY FOR BEGINNERS 



CHAP. 



are found on the stem, leaves, and flowers of most plants. 



The unicellular root -hair is produced by the outgrowth of an 



epidermal cell. 



On the surface of the stinging nettle a very large number of 



hairs are produced. If one is examined by the microscope it is 



seen to consist of a single cell at the apex ; the base of this cell 

 is fixed in a number of cells which be- 

 long to the epidermis. The tip of the 

 hair of a stinging nettle is strengthened 

 with silica, while the rest of the hair con- 

 tains carbonate of lime. In the ter- 

 minal cell a poisonous fluid is produced. 

 When an animal touches the plant the 

 stiff pointed hairs enter its skin and the 

 poisonous fluid is poured into the wound. 

 The well known smarting sensation 

 which a person feels when "nettled" is 

 due to this acid fluid. The well known 

 method of rubbing the wound with a 

 Dock leaf is to neutralise the acid with 

 the alkaline secretion present in the 

 Dock leaf. 



Emergences. Emergences are 

 modified portions of the epidermis 

 which may act as glands. A gland 

 is an organ which secretes some sub- 

 stance from the materials which are 

 brought to it in the cell sap. The ten- 

 tacles of the Sundew are well known 

 examples. These secrete a substance 

 very much like the gastric juice of the 

 higher animals, and this secretion en- 

 ables the plant to digest any insects 

 which the plant may catch. 



EXPT. 87. Cut sections from a Turnip or 

 from a Potato ; mount the thinnest in water. 

 Note 



(i) The shape of the cells. They are 

 parenchyma cells. 



(ii) The contents of the cells. These consist principally of 

 protoplasm and starch grains. 



FIG. 126. Stinging hair 

 cf Nettle. (X6o.) (S.) 



