28 NATURE STUDY 



the roots washed off and thus much be learned in regard to the 

 root systems. If caving banks, washouts, railroad cuts or other 

 excavations allow the observation of the roots of larger plants at 

 greater or less depths under ground, the teacher of course will 

 take advantage of them. Professor Hilgard has published in a 

 bulletin of the Department of Agriculture of California, the pho- 

 tographs of excavations showing the extensive root system of fruit 

 trees as they are disposed in California to meet the requirements 

 of its peculiar seasons. 



Two objects of great importance can easily be observed in 

 the growth of the plants between the glass sheets and in the water 

 jars they are the root hairs and the root tip with its root cap. 



The root hairs are the parts that absorb the water and hence 

 their importance. The main purpose of the root system is to ex- 

 tend the parts that bear the root hairs into every cubic inch of 

 soil where moisture can be obtained within reach of the plant. 



The root hairs form a fine down ol minute hairs as thin as 

 filaments of cotton which cover each small rootlet a short distance 

 back of the growing tip of the rootlet. They are so delicate that 

 they usually break off when a plant is pulled up by the roots. 

 They can be seen with the naked eye, but, of course, a lens shows 

 them better. 



The root tip is also a very important organ of the plant since 

 it is by the root tips that the roots are planned out and each carried 

 to the place where it comes finally to lie. That is, the root tip is 

 the growing end of the root. It is very sensitive to contact, to 

 moisture and also must be to other influences. It is, in conse- 

 quence, able to find its way to the parts of the soil where it should 

 go and in doing this is able to avoid the various obstacles which 

 it meets. At its very tip it is covered with a minute cap called 

 the root cap which affords the extreme end some protection. 



Have the pupils see thru the glass sheets how the root 

 tips avoid the obstructions and find their way in different direc- 

 tions. Root tips avoid light, while stem tips seek it. Root tips 



