HOW PLANTS ARE INFLUENCED 341 



a stock which supplies it overabundantly with water 

 forms a mass of large -celled wood -parenchyma in place 

 of ordinary wood. 



It is often very noticeable that the leaves which are 

 formed during a dry period are small and stunted, 

 while those subsequently formed on the same branch 

 during a rainy period may be four or five times as 

 large. 



The roots of many plants branch in a peculiar, 

 compact fashion when they grow in water (for example, 

 the roots of trees when they enter a cistern or drain- 

 pipe), hence the popular name, " water-roots." 



Very interesting results are obtained when we grow 

 ordinary land -plants in a saturated atmosphere, in the 

 manner shown in Fig. 157. Select a bulb (or corm, 

 tuber, etc.) which has begun to sprout: cut out a piece 

 (two or three inches long) bearing a sprout at one end, 

 place it in a dish, and cover it with a lamp-chimney. 

 Pour in some water, and cork the chimney, covering 

 the cork with sealing-wax or vaseline. The air within 

 the chimney will soon become saturated with moisture, 

 and its influence on the growth of the plant can be 

 readily observed. The tissue at the base, which is in 

 contact with the water, will eventually decay; but this 

 will not interfere with the growth of the sprout. The 

 results of growing Dandelion leaves and Gorse in this 

 way are shown in Figs. 197 and 198. 



Water seems to have a direct influence on the pro- 



