STUDIES OF IRRITABILITY OF PLANTS PEIRCE 63 



experiment lasting only a few minutes or at the most an hour or two, it 

 ought not to be trusted longer. An experiment which lasts a week or even 

 months increases in value as it lasts, if it had any value at the start ; and 

 the failure of the apparatus at the end of six months entails a loss much 

 greater than more serious mechanical difficulty within a day or two of the 

 beginning. The cost, unreliability and the wearisomeness of winding a suit- 

 able number of separate instruments drove me to consider other apparatus. 

 And by devising new apparatus I tried to ascertain the dominating reason 

 for the persistent dorsi-ventrality of the thalli of Fimbriaria and of the pro- 

 thalli of Gymno gramme. 



To Professor W. F. Durand, head of the Department of Mechanical 

 Engineering, is due all the credit for structural details and for supervising 

 the construction and the successive modifications of the apparatus in the 

 Mechanician's Shop of this University. And I take this opportunity to ex- 

 press my most grateful appreciation of his skill in divining what I wanted 

 and his untiring help and unflagging patience in securing it. As a detailed 

 description of the apparatus would be more appropriate elsewhere, I may 

 here content myself with a statement of its essential features. 



The apparatus may be called a multiple clinostat. As my experiments 

 involved the turning of cultures in a horizontal plane upon a vertical axis, 

 the apparatus began with a set of twenty-five turn-tables on five shelves built 

 into the embrasures of each of three windows, the turn-tables in each window 

 revolving at different speeds, but all the turn-tables in one window turning 

 at the same rate. The actuating mechanism consisted of a clock-work driven 

 by a heavy weight and controlled by a fan governor. This actuating mech- 

 anism was connected by a series of belts and shafts with the batteries of turn- 

 tables. Experience, however, has led to the gradual and final elimination 

 of all belts. Chains and sprockets were first substituted for belts. Finally 

 these were replaced by direct gears. This made possible the consolidation 

 of the cultures into one window, there being five rows of ten turn-tables each 

 on a set of shelves in the window nearest the clock-work and connected with 

 it by a shaft with bevel gears. This shaft is horizontal and runs from the 

 clock-work, bolted to a table, which is itself bolted to the floor, to a vertical 

 shaft at one side of the window. At each shelf this vertical shaft carries a 

 gear which engages a corresponding gear carried on the axle of the nearest 

 turn-table. The margin of this turn-table, and of all the others in the row, 

 is toothed, and the turn-tables are so set that the movement of one of them 

 sets all the others into similar motion. All the turn-tables in a row move at 

 the same rate, but the rate of each row is determined by the ratio of the gear 

 on the vertical shaft to that of the first turn-table in the row. It is possible, 



