Reaction to Gravity in Fronds of Asplenium bulbiferum . 57 
After about eight pairs of leaflets are unfolded, the presentation time 
is much more difficult to measure, owing to the fact that all the varied 
types of movement previously 1 described may, and often do, take place— 
some to an increased degree—until maturity is reached. Nutation is 
probably at its maximum, and, although varying greatly in amount, may 
be as much as 20° right and left of the vertical. Growth in the dark of 
course avoids heliotropism, and control experiments have been made in 
a dark room ; but here constant conditions, particularly the important one 
of temperature, could not usually be obtained. 
Physiological variability of individual fronds finds expression in the 
different angular heights attained ; for however morphologically similar 
several fern fronds may be, they will almost certainly not behave identically 
under precisely similar conditions. Hence the presentation times deduced 
should be regarded as those periods which, under the given conditions, will 
generally produce movements of about 5 0 and only very rarely exceed¬ 
ing io°. 
Tables showing results of experiments at various stages of the 
fronds development. 
Temperature 20° C. (approx.); humidity 85 % (approx.). 
P. T. = presentation time. 
L. T. = latent time. 
Stage: Early Infant (apical coil just above soil level). 
Length of frond 
in cm. 
Period of stimu¬ 
lation in hours. 
Angle of Latent time 
curvature . in hours. 
i*5 
0.8 
1.6 
1.2 
8 
71 
P. T. = 8 hours; L. T. 
16 hours. 
16 
16 
Stage: Early Infant (apical coil about a centimetre 
J *5 
4 
IO° 
J-5 
4 
0 
0 
I, 5 
4 
4° 
2 -3 
4 
— 
27 
Si 
— 
2-6 
3 
— 
above the soil). 
10 
10 
10 
P. T. = 4 hours ; L. T. = 10 hours. 
Stage: Middle Infant. 
5 * 2 
3 
3 
n° 
5-o 
10° 
3-o 
O 
O 
„o 
7 
3-4 
'j 
O 
_ 0 
5 
3-8 
3 
0 
5 
3*° 
3 
— 
3*° 
3 
— 
P.T. = 3 hours; L.T. = 8 hours. 
1 Prankerd : loc. cit., p. 144. 
