Page:Researches on Irritability of Plants.djvu/32

Rh varying effects of freshness and fatigue, of stimulating or depressing drugs, of heat or cold, of the environment, are in this way clearly revealed by the characteristic flexures of the curve. Thus, by means of testing-blows, we are able to make the plant itself describe those obscure internal changes which would otherwise have entirely escaped us.

In fact, the phytographic records would, in the case of plants, supply us with all the information that myograms afford in the case of animal tissues. The experimental difficulties which the plant offers are, however, very great. In the case of muscle-contraction, the pull exerted is considerable and the friction offered by the recording-surface constitutes no essential difficulty, though even here the time-relations of the curve are, I have reason to think, rendered somewhat unreliable by this friction. In the case of plants the contractile movement is relatively feeble, and in the movement of the leaflet of Desmodium, for instance, a weight so small as four-hundredths of a gram is enough to arrest the pulsating leaflets. When employing the very lightest lever, the extremely minute friction offered by the smoked-glass surface of the recording-plate is sufficient in this case to cause complete cessation of the record. Even in the leaf of Mimosa, the friction offered is enough to distort the curve to such a serious extent that errors are introduced into the amplitude and time-relations amounting to more than 50 per cent. These difficulties have been overcome by the successful devising of my Resonant Recorder, an account of which will form the subject of the next chapter.

Obscure modifications of internal condition of plant, resulting from changing factors of environment, may be revealed by records of plant's response to testing-blows.

The relation between the impinging stimulus and the