144 



through the p. m. and early night, when a minimum was reached. After this the 

 pressure increased until it attained the maximum during the following a. m. 

 Sachs further showed that the periods of maximum and minimum pressure were 

 independent of small variations in temperature. 



The work of Sachs was done by the use of crude instruments that i-equired 

 constant attention, and it seemed that an instrument of precision, making auto- 

 matic records, would enable one to add something to the work already done on 

 the subject of root pressure. In 1890 a rude instrument was made of wood and 

 iron, and some few experiments conducted on the subject. Later a machine of 

 more accurate working was constructed at the college workshop in Crawfordsville, 

 and this formed a pattern for the one made at Lafayette under the supervision of 

 Dr. Arthur. In the evolution of the apparatus to its present condition changes 

 have been introduced that brings the machine into a form easily used by the 

 average student and capable of giving accurate results. 



For our work on the subject of root pressure many plants were grown from 

 seeds in the greenhouse, and were used when the stems were 4-5 mm. in diameter. 

 With those plants secured from out of doors or at other green houses, they were 

 brought in weeks before the experiments and given ample time to adjust them- 

 selves to any changes in their surroundings. The results show that the latter 

 plants corresponded in their records with those grown in the green house from 

 seeds. For the experiments the attachment of the plant to the machine was 

 made in the usual way under water, and the apparatus placed on an iron pier to 

 prevent jarring. The records of temperature were made by a self-recording ther- 

 mometer. The clock used in the root pressure machine would run for eight days, 

 and an experiment when properly started needed no attention until its comple- 

 tion, or until the time when the pressure was insufficient to show itself on the 

 rods of the instrument. The increasing weight of the column of mercury usually 

 produced this result in 4-5 days. The smoked .rods with the record of the peri- 

 odicity were placed on sensitive paper, and the lines printed for permanent pres- 

 ervation. Temperature cards were preserved along with these for comparison. 

 The plants experimented upon were fuchsia, bean, geranium, grape, sunflower, 

 tomato, etc. 



Occasionally upon the attachment of the plant a decided negative pressure in 

 the stem would be observed. This was especially noted in the grapevine growing 

 out of doors, where the records were made. The negative pressure was so great 

 that the water and part of the mercury were pulled down into the stem and the 

 particles of mercury could be found in the ducts upon splitting the twigs an inch 

 or more from the top, where the attachment was made. This phenomenon was 



