Page:Researches on Irritability of Plants.djvu/30

Rh shortening might be accomplished by attaching the thread nearer to the fulcrum. Proceeding in the manner indicated, any magnification, however high, can be obtained.

Reduction, again, may be effected with equal ease. When the point of attachment is exactly midway between the pulvinus and the tip of the leaf, then the movement executed by it will be half that described by the extremity of the leaf. By bringing the point of attachment nearer to the pulvinus, we can obtain whatever reduction may be required.

The resultant magnification or reduction of the record will thus depend, in any given case, on two factors—namely, the relation between the length of the writer and the length of the lever-arm, on the one hand; and, on the other, the relation between the distance of the point of attachment from the pulvinus and the entire length of the leaf.

Thus if the lever produce a magnification of four, and the point of attachment cause a reduction to half, the resulting magnification will be 4 X $1⁄2$ = 2. As the movement of the primary petiole of Mimosa is considerable, the records taken are normally either equal or reduced to two-thirds. A record taken in this manner is given in fig. 2. The height