The Root and the Soil. 65 



after planting, we may see that the main roots start 

 above the point at which the stem was originally attached 

 to the seed; and if we pull np a pumpkin vine or an un- 

 trellised tomato plant late in summer, we often find it 

 rooted from the stem at some distance from the original 

 root. Lateral roots originate in the internal tissues of 

 the stem or root and not close to the surface, as do buds 

 (132). 



89. Moisture Excites Root Growth. Boots develop, as 

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

 a certain time in contact with abundant moisture. In 

 the pumpkin \'ine 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 ^Nith 

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

 the air is nearly saturated with Avater, 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 Ban- 

 yan 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, f root promptly when their stems 

 are immersed in water. 



90. 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 



* Ficus Indica. f Tropceolum. 



