upon the subject. A brief account of the methods and resuFts of 

 this undertaking is here given. All of the experiments here 

 described were made on plants growing in pots in the Botanical 

 Laboratory, or in the adjoining rooms, or in a large conservatory 

 window, where the conditions of light, heat and moisture were 

 favorable to the healthful growth of the plants experimented upon. 



In conducting the experiments I have been greatly aided by 

 Instructor W. A. Henry, of the Botanical Department, who has 

 also rendered much assistance in collating information relating to 

 the whole subject. 



Experiment No. i. — A strong plant of strawberry geranium 

 (Saxifraga sarmentosa) has been allowed to become infested with 

 .green aphides. They are mostly confined to the flower pedun- 

 cles and young tips of the runners. 



May 13. — The plant is thoroughly sprinkled with dilute yeast by 

 means of a flat paint brush so that all parts, especially those cov- 

 ered with aphides, are fairly wet. The yeast used is fresh domes- 

 tic yeast, diluted with two-thirds water, Torulse are active, as is 

 shown from the fermentation in progress. After being sprinkled 

 the plant is placed by itself on a table and covered by a large 

 funnel-shaped hood, made of thin white paper, slightly open at 

 the bottom to admit air. A cup of actively fermenting yeast is 

 placed at the side of the plant under the hood, so that any germs 

 which may possibly escape from the yeast will be confined to the 

 air immediately surrounding the plant. Some of the older leaves 

 are infested with a number of scale insects. 



May 15. — No dead aphides are to be found. Some cast-off 

 skins from molting are seen. 



May 18. — Peduncles and tips of runners are loaded with plump 

 aphides. Many cast-off skins. No dead insects are found. The 

 scale insects larger and apparently more numerous. 



May 20. — All young parts completely covered with aphides. 



June 3. — The plant is obviously injured from attack of aphides 

 and scale insect. Some of the leaves are dead. The plant is out 

 of flower and the peduncles are more or less withered. On these 

 peduncles are a number of dead aphides. These might have 

 starved for want of food, owing to the drying up of the juices of 

 the peduncles. A number of dead aphides are examined under 

 the microscope in a variety of ways, but in no case is there any 



