1 86 METHODS IN TEACHING 



marked inclination to follow the apparent diurnal motion 

 of the sun. The leaves of many plants, notably oxalis, 

 varieties of acacia, anemone, and lupines are folded at night 

 or during stormy weather. The movements of twining 

 plants, such as the morning-glory, pole-beans, and others 

 can be studied easily from plants in boxes in the school- 

 room. When such a plant begins to " run," it takes a slow 

 revolving motion, the tip feeling for some support upon 

 which to climb. As soon as this is found the twining mo- 

 tion begins. What is the direction of this motion? Is it 

 similar or opposite to the motion of the hands of a clock? 

 Do any plants twine in the opposite direction? 



The motion of tendrils in such plants as peas, grapes, 

 passion vines, wild cucumber, and pumpkin is also easily 

 seen. Leaf stems of some plants are similarly sensitive and 

 act as tendrils. The nasturtium is a familiar example. 

 Root tips show a marked sensibility. This enables them to 

 seek the line of growth that offers the least resistance in 

 their extension into the soil, also to locate plant food even 

 at a considerable distance. The following is a simple ex- 

 periment that will illustrate the movement of root tips: 



Suspend several peas or beans in a moist box until they 

 begin germinating. To the growing points of the roots of 

 two or three attach a very small bit of thin card by means 

 of a little mucilage or glue. Note that the root tips so 

 treated tend afterward to grow toward the bit of card, re- 

 sulting in very crooked roots. The roots of the others 

 grow straight downward. 



There are tramps and paupers in the vegetable world; 

 they are the parasites. Through parasitism they have long 



