36 V NATURE TEACHING. 



size : see plants of maize, grasses, palms, etc. 



2. In dicotyledonous plants, on the other 

 hand, increase in thickness may -go on for a 

 very long time, and the roots in consequence 

 become very thick. Take any opportunity of 

 observing the roots of trees, for example, 

 bread-fruit, mango and others in which the 

 main roots are often as thick as the branches 

 of the stem. Interesting cases showing an 

 enormous increase in the thickness of roots 

 will readily be seen in plants of radish, 

 turnip, beet and cassava. 



GROWTH IN LENGTH. 



1 Germinate some beans in moist sand 

 or sawdust and allow them to grow until 

 their roots are about two inches long ; wash 

 carefully a number of the seedlings and select 

 one which has a straight, well formed root, 

 perfectly free from injury. 



2. Lay the seedling on a piece of damp 

 blotting paper and, alongside it, a piece of 

 cardboard, so arranged that the surfaces of 

 root and cardboard are on the same level. 

 With a fine camel's hair brush and Indian 

 ink make a number of fine lines on the root, 

 and a corresponding set on the cardboard, 



