Studies in the Geotropism of Pteridophyta*.-IV. On Specificity in Graviperception.

Abstract

Summary. 1 The work is based on some 2300 experiments on seven species of the genera Asplenium and Osmunda, and gives the quantitative reaction to gravity of the fronds at stages previously defined as infant, adoleFcent, and mature (Waight, 1923). 2 Specific differences in the presentation time are distinct, in all buI one case, though slight coinpared with the generic differences, which are measured in hours for Asplenium and minutes for Osmunda. 3 O. cinnamonlea is believed to be the most sensitive plant to the force of gravity as yet discovered, since its fronds, at inid-adolescent stnges, will respond to a stimulus lasting ody 20 seconds. 4 The latent time shows relatively little specific difference, bnt is strikingly distinct generically. Osmunda responds about three times as quickly as Asplerzium. 5 Presentation time and latent time for ferns may be represented by physiological graphs here termed grnviscripts; and certain generididions with regard to them are suggested. 6 The data at present available point to latent time as in general a far more constant quantity than presentation time. In a fern frond it is at its minimnm, and approximately constant throughout the adolescent stages. 7 It is pointed out that, since all characters possess taxonomic value in a truly Natural System, in cases of doubtful affinity, where easily available criteria have been found inconclusive, recourse may be tiad to physiological data.