Reaction to Gravity in Fronds of Asplenium bulbiferum . 61 
Summary. 
1. The fronds of Asplenium bulbiferum exhibit a grand period of 
irritability to gravity as measured by presentation time. This corresponds 
with the stage of development of the frond and not directly with its age or 
length. 
2. At 20° C. and 85 per cent, humidity the presentation time decreases 
from eight hours at a very early stage of development to a minimum of 
half an hour when the fifth to seventh pairs of leaflets are unfolding. It then 
rises to about six hours, when response to gravity ceases, a little before the 
frond is mature. 
3. The latent time shows a range of sixteen to five hours and is also 
affected by the stage of the frond, but to a much less extent than the 
presentation time. The ratio between the two periods increases until both 
are at their minimum value, when it again decreases. 
It is hoped to extend the present work to other ferns, and to ascertain 
the effect of temperature and other factors upon the time periods studied. 
My thanks are due to Mr. Lacey, of the South-Western Polytechnic, 
and Prof. R. C. Maclean, of Cardiff University, for the loan of excellent 
klinostats, and to Prof. W. Stiles for affording me the opportunity of carry¬ 
ing out this research in his laboratory. I also wish to thank Miss Prankerd 
for all her help and kindness, without which it would have been quite 
impossible for me to have done this work. 
