2570 Journal of Applied Microscopy 



from above and is covered by a large plate of glass. A glass filament, not 

 thicker than a horse-hair, and from 3 to 5 cm. long, is fastened to the end of the 

 stem by means of shellac dissolved in alcohol. If the solution be allowed to 

 evaporate until it becomes so thick that it will set hard in two or three seconds, 

 it will not injure the tissues. The end of the glass filament bears a very small 

 bead of black sealing-wax. Below the bead is a small triangular piece of white 

 paper, whose exact center is pierced by the filament. The bead and the paper 

 triangle are viewed through the horizontal glass plate, and when the bead 

 exactly covers the center of the triangle, a dot is made on the glass plate with a 

 sharply pointed stick dipped in India ink. Make other dots at short intervals 

 of time and join the successive dots with straight lines. In this manner a trac- 

 ing of the movement of the stem tip will be obtained. 



The circumnutation of twining plants can best be studied in-doors, where the 

 wind does not interfere. On some twining plant select a shoot which has found 

 no support, and whose apex has a large open hook. Thrust into the earth a 

 wooden rod, and to its upper end tie the selected shoot, allowing the terminal 

 15 to 30 cm. of the shoot to project beyond the support. Place beneath the 

 plant a sheet of white paper, and on it mark from time to time the position of 

 the hook of the shoot, determining thus the direction and time of revolution. 



Find other shoots that are twining about supports, and see whether the revo- 

 lution of their tips has the same period as that of the free shoot. 



Examine carefully the shoots that have twined and see whether the shoot 

 shows torsion in climbing. 



In concluding this series of articles, the writer feels constrained to take this 

 opportunity of expressing his thanks for the appreciative manner in which they 

 have been received by a large body of teachers, and also to the editor of this 

 Journal for his painstaking care in presenting them to the reader in the best possi- 

 ble form. The aim, in giving these methods, has been toward practicability rather 

 than originality. Although they come from a university laboratory, yet it is be- 

 lieved that many of them are well adapted to use in secondary schools. The 

 writer will be very grateful to receive any criticisms or suggestions for making the 

 methods more accurate and practical, and will be glad to give his attention to 

 inquiries regarding them. Howard S. Reed. 



University of Missouri. 



