Reaction to Gravity in Fronds of Asplenium bulbiferum. 59 
Stage : Adolescent f- ( approx .). 
Length of frond 
Period of stimu- Angle of 
I^atent time 
in cm. 
lation in hours. curvature. 
in hours. 
17-5 
3f io° 
6 
16.2 
02 t 
17-0 
■jl 1-0 
02 l 
16.5 
3 — 
18.7 
21. _ 
— 
19*5 
2 1 
J 2 
P. T. = 3! hours ; L. T. = hours. 
Stage : Adolescent § (approxl). 
30.0 
A 1 c ° 
42 5 
P. T. = 4|- hours; L. T. = 7 hours. 
Stage : Adolescent § (approx.). 
7 
13-5 
6 5 ° 
8 
32.0 
5 § 
P. T. = 6 hours; L. T. = 8 hours. 
— 
From the above tables it will be seen tha* the presentation time is 
eight hours at a very early stage in the life of a frond, and decreases during 
its development until it reaches a minimum of half an hour, when the fifth to 
seventh pairs of leaflets are unfolding, rising again until all irritability to 
gravity ceases, when only the rudiments of the last two or three pairs of 
leaflets remain in the apical coil. Towards the end of its existence geotropic 
response is expressed by a twist of the rachis in its own plane, since the 
strong epinastic curvature taking place at this time seems to prevent any 
upward movement of the frond. 
The above facts are shown graphically (p. 60) by plotting the pre¬ 
sentation times and latent times as ordinates, and the stages of the frond 
as abscissae. The latter must of necessity be somewhat arbitrary, and can 
only correspond approximately with periods of time, as the rate of growth 
of a frond depends largely on temperature, which could not be kept constant 
through the six weeks or so of its development. 
In the course of the work it was found that the presentation time in 
the Late Adolescent stages bore a more constant relation to the proportion 
of leaflets unfolded than to the actual number; hence the later stages 
are represented as fractions which express approximately the ratio of the 
number of leaflets unfolded to the total number possessed by the frond. 
The curve for latent time has been plotted from the average of the 
figures in column 4 of the tables. It follows in general the curve for 
presentation time, being similarly affected by the stage of development of 
the frond, but not nearly to so great an extent, since its range is only 
sixteen to five hours as against eight hours to half an hour. This seems 
to be in accordance with the view expressed by Jost, 1 that distinct sets of 
phenomena are involved in perception and reaction. 
1 Jost, L. ( 1907 ): Lectures on Plant Physiology, p. 441. 
