To find the cfifect of light upon the growth rate in plants, place one of two 

 pots of growing seedlings or of sprouting potatoes in a light room and the other 

 in a dark closet. Keep all the conditions except the intensity of light the same. 

 Compare growth after a few days. Record difTerences and account for the results. 



To find the relation of gravity to the direction of growth of roots and shoots, 

 place several soaked seeds on moist blotting paper between two large panes of 

 glass so that they may be observed. Fasten the panes in vertical position with 

 bottom edges resting in a tray of water. With a wax pencil mark the positions of 

 the roots and of the shoots when they appear. Then turn the arrangement one 

 fourth of the way around and allow to stand in tray for two days more. Mark 

 the position of each shoot and each root daily. Turn the arrangement one fourth 

 of the way around further and again mark positions of roots and shoots. How do 

 the roots and shoots respond to the shifts in position? 



3 To find the effect of growth-modifying substances on the growth-response 

 of plants to light, place several vigorous potted plants of the same kind in a 

 window and apply the material to all but one of them, on the side of the stem 

 exposed to the light.^ After a week or so, compare the plants for any difference 

 in growth. 



4 To study the responses of organisms to stimuli, observe the behavior of 

 paramecia through the microscope, while changing the physical and chemical 

 conditions surrounding them.' 



To find the response of paramecia to changes in temperature, bring into con- 

 tact with the slide on which the animals are mounted a clean slide that has been 

 heated by moving it back and forth above a low flame, and watch the animals as 

 they are slowly warmed. Cool the slide by placing an ice cube on one end of it. 

 How do changes in temperature afFect the behavior of the animals .f" 



To find the response of paramecia to acid, place a drop from a test tube of 

 water through which carbon dioxide has been bubbled (from the lungs or from 

 a generator) near the drop in which the paramecia are swarming. Draw the two 

 drops together with a pin and note the changes in the behavior of the animals. 

 Describe the response. How can this response be related to the animal's method of 

 getting food? 



To find the response of paramecia to electricity, place about 50 cc of the culture 

 in a shallow dish, and at opposite sides of the dish insert two carbon rods that are 

 attached by wires to the two terminals of a 6-volt battery. Describe the reaction of 

 paramecia to the electric current. Do they migrate equally toward both poles, or 

 away from both poles, or toward one pole and away from the other? 



^Use indole-acetic acid or naphthalene-acetic acid as growth substances. Prepare mixtures 

 in following proportions: (1) 10 mg growth substance to 1 g lanolin; (2) 2.5 mg to 1 g; 

 (3) 0.6 mg to 1 g; (4) 0.15 mg to 1 g. Dip a glass rod into each preparation in turn and 

 touch it to side of stem of one plant. 



-Prepare a hay infusion by tying a double handful of hay in a cheesecloth bag and sus- 

 pending it in a gallon jar of water. After this has rotted for one week, add some water 

 collected among vegetation along the edge of a pond. In about two weeks the top of the hay 

 infusion should be teeming with paramecia. 



27\ 



