PREFACE
I have in this work dealing with my researches on the irritability of plants introduced new methods by which the scope of investigation has been enlarged, and a very high degree of accuracy secured. In my previous treatise on Plant Response, the response recorder employed was a modification of the optical lever, automatic records being secured by the very inconvenient and tedious process of photography. The delay thus imposed retarded seriously the progress of the research. Those practically engaged in investigations on plants can realise the difficulties that arise from the too quick passage of the seasons. It thus frequently happened that by the time new instrumental appliances were rendered practicable the favourable season for the plant was over, involving the postponement of the experiment for another year. In spite of these difficulties, the long series of investigations that I then carried out gave many interesting results, which not only threw light on many obscure problems, but also led to the discovery of several important phenomena in plant physiology.
Some of these results, moreover, tended to cast doubt on certain conclusions that had found universal acceptance. It has, for example, been held that there was no transmission of true excitation in Mimosa, the propagated impulse being regarded as merely hydro-mechanical. The question whether the transmitted impulse was physical or physiological could only be satisfactorily decided if the plant could itself be made to record the velocity of its impulse and the changes induced in that velocity under physiological variations. This is but one out of several
