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The sensitiveness of the method as demonstrated in 

 this instance leaves nothing to be desired, but it would 

 be less convenient for investigating the growth of larger 

 organs or whole plants ; in such a case we have to 

 use the second of the methods indicated, i.e. instead 

 of magnifying the growing organ itself, we magnify 

 only the motion of the growing parts. We use for 

 the purpose an apparatus, the main part of which 

 consists of an index fixed to the axis of a small pulley 

 (fig. 56, I, a) . Over the pulley a silk thread is thrown to 

 one end of which a small weight [h) is attached, and to 

 the other a small hook (c) made of thin wire. Catching 

 the apex of any stem with the hook (a small wound 

 as the result of the prick will not do it any harm) we 

 let the weight hang freely on the other side of the pulley, 

 and pull down the silk thread. Let us now suppose that 

 our stem has grown a little ; what will be the conse- 

 quence ? In growing, the stem will slightly loosen the 

 silk thread, and the weight will fall as far as the plant 

 has grown ; at the same time the silk thread lying close 

 to the pulley will oblige it to make a turn of correspond- 

 ingly insignificant magnitude owing to the friction it 

 exerts upon it. With the pulley the index will also turn ; 

 but its point will naturally trace a much wider course, 

 so that an imperceptible movement on the part of the 

 tip of the growing stem will cause an already very 

 considerable movement of the index point. This latter 

 movement will exceed the former as many times as the 

 length of the index exceeds half the diameter of the 

 block. In our apparatus half the diameter of the block 

 is equal to two millimetres, the length of the index is 

 twenty-centimetres, i.e. a hundred times as much ; 

 therefore every increase in the length of the stem 

 will be shown by a movement of the point of the 

 index a hundred times as great. The advantage of 

 this instrument is obvious. We may fasten behind the 

 index a circular scale with divisions, like those on a clock, 



