On the Presentation Time and Latent Time for 
Reaction to Gravity in Fronds of Asplenium 
bulbiferum. 
BY 
F. M. O. WAIGHT 
{Associate of University College , Reading). 
With one Diagram in the Text. 
I T has already been shown 1 that fronds of Asplenium bulbiferum are 
negatively geotropic, and further that the specific irritability is not 
constant throughout their development. 
In 1921 Miss Prankerd suggested to me that some measure of the 
intensity of this irritability might be gained by ascertaining the presentation 
time at different stages of development, and this I have attempted to do 
under her direction. 
The presentation time as defined by Czapek 2 is the shortest period of 
stimulation which will produce any response on the klinostat, and the latent 
time is the period elapsing between the beginning of stimulation and the 
first indication of response. In this case, therefore, the presentation time is 
the period of horizontality necessary to secure the slightest movement 
upwards of the frond, and the latent time is the period from the beginning 
of horizontality to the moment when the movement is just visible. The 
first two stages in the development of the frond previously noted, 3 namely, 
Infant, when the leaflets are in the apical coil, and Adolescent, when the 
leaflets are unfolding, have been further subdivided into Early Infant, 
fronds 08-3-0 cm. ; Middle Infant, fronds 3*o~5*5 cm. ; Late Infant, fronds 
over 5*5 cm. with no leaflets unfolded ; and Adolescent 1, 2, 3, &c., according 
to the number of pairs of leaflets unfolded from the apical coil. 
The ferns were grown in a greenhouse, and although it was impossible 
1 Prankerd, T. L. (1922) : On the Irritability of the Fronds of Asplenium bulbiferum , with 
Special Reference to Graviperception. Proc. Roy. Soc., B., xciii. 
2 Czapek (1898): Jahrb. f. wiss. Bot., xxxii. 
3 Prankerd: loc. eit., p. 144 . 
[Annals of Botany, Vol. XXXVII. No. CXLV. January, 1923.] 
