66 Principles of Plant Culture. 



in the internal tissues of the stem or root and not close 

 to the surface, as do buds (131). 



88. Moisture Excites Root Growth. Roots develop, 

 as a rule, from portions of the stem that are maintained 

 for a certain time in contact with abundant moisture. 

 In the pumpkin vine and tomato plant above mentioned, 

 nearness to the soil furnishes a moist atmosphere. A 

 corn stalk pegged down to the ground for some distance 

 will usually root at all joints of the stem in contact with 

 the soil. A potato plant grown under a bell-jar, where 

 the air is nearly saturated with water, will form roots 

 at any joint of the stem. In parts of the tropics where 

 the air is very moist, certain plants, as orchids and the 

 Banyan tree,* emit roots freely from the stem above 

 ground. Cuttings (358) and layers (349) form roots 

 because they are maintained in contact with abundant 

 moisture and at a suitable temperature. Cuttings of 

 some plants, as the willow and nasturtium,! root 

 promptly when their stems are immersed in water. 



89. Oxygen is Necessary to the Life of Roots. Since 

 the cells of newly-formed roots are filled with proto- 

 plasm, they must have access to the oxygen of the air, 

 or they can neither live nor grow. This is shown by a 

 simple experiment. Boil a quantity of water fifteen 

 minutes or longer, to exhaust it of free oxygen, and then 

 cool it quickly by setting the dish containing it in cold 

 water. Now place a healthy cutting (358) of some 

 plant that roots freely in water, as willow, nasturtium 

 or wandering jew,| in each of two tumblers. Pour a 

 part of the cool, boiled water into one of the tumblers 



* Ficus Indica. t Tropoeolum. % Tradescantia. 



