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how long a time is wanted for a certain increase, in contrast with 
the “microscopical” method, where direct growth in a certain lapse 
of time is measured. 
When this apparatus was practically constructed, my attention 
was called to a paper by Bovis’), who has already put into prac- 
tise the same device for an auxanometer. His method has several 
disadvantages. In the first place the linkage by means of an invar- 
thread is detrimental to the plant and in the secoud place the con- 
nection between plant and apparatus is by no means a rigid one. 
The chief disadvantage, however, lies in the fact that the plant 
itself closes the circuit, which effects the upward movement of the 
contact. This current, activating an electro-magnet, must be of a 
rather high voltage. Therefore it, inevitably, will emit sparks at the 
opening of the cirenit. These sparks will burn the contact-metals, 
causing an inconstancy in the place of contact. Bovir’s auxanometer 
records on a drum, revolving at a velocity of 1 m.M.a minute. At 
each contact a pen makes a check on the drum. The distance 
between two checks thus corresponds to the time, wanted for a 
certain growth. Apart from the tedious counting of checks and mea- 
suring their distances, the slow movement of the drum leads to 
high errors in taxation. 
Moreover, Bovim didn’t design his machine for our purposes; it 
meant to be a precision-machine for demonstration. Some years 
afterwards he describes *) a simplification of his apparatus, whereby, 
however, it has lost much of its accuracy. 
To obtain a high grade of accuracy, many obstacles had to be 
overcome. The whole apparatus has been constructed by Mr. P. A. 
pe Bouter, mechanic at the Botanical Laboratory of the University 
of Utrecht, from whose knowledge of engines the writer owes 
many ideas. The writer wants to render him his best thanks for 
the constant energy, with which he carried out his work. 
The Auaanometer is mounted on a working-axis (1) (See fig. 1), 
18 ¢.M. in length, that may be fixed on a clinostat-table (2). In 
order to revolve the. plant vertically in regard to its revolving-axis, 
a side-axis (8) may be fixed on the working-axis (1). The test-plant, 
growing in a little pot of zine (3 e.M. high and 4 c.M. diameter) 
may be fixed on a movable little table (4) by means of a handle 
(6) of the cover. 
This handle (6) is fixed by a single screw (7), so that there is 
an unmovable connection between plant, pot and table. 
1) W. T. Bovis. Bot. Gazette, 1912. 53. 
3) W. T. Bovis.’ Am. Journal of Bot. 1915. 2. 
