Irritability of the Pollen-presentation Mechanism in 
the Compositae. 
BY 
JAMES SMALL, M.Sc. (Lond.), Ph.C., 
Assistant Lecturer in Botany , Bedford College, London University. 
I N view of the frequency with which this phenomenon has been found 
during the past year in the Compositae and its appearance in several 
common British species, it has been thought advisable to publish this 
preliminary list of irritable species and varieties. The data form part of 
a thesis in course of preparation, therefore they will not be discussed 
fully. The present contribution aims only at recording those species in 
which irritability has been observed for the first time. 
Few previous authors have recorded the exact type of irritability, 
and none has recorded the degree of irritability observed (1-8 and 11), 
but in the present list those hitherto neglected features of the phenomenon 
are recorded thus : 
Types of Irritability . 
A : pollen presented on touching ; no lateral movement of the anther tube. 
B: „ 
n 
5 > 
; lateral movement, indefinite in direction. 
C: „ 
5 > 
?> 
; lateral movement towards the touch. 
C‘: „ 
1) 
>> 
>> 
; lateral movement towards the centre of 
the capitulum. 
C° ; „ 
>> 
>> 
>5 
with more or less explosive rapidity. 
The degree of irritability is noted as slight when it requires careful 
observation, and notes are added on special cases. 
The phenomenon has been well known in the Cynareae since the 
seventeenth century at least, but very few records are to be found in the 
literature of the subject of irritable species , even in the Cynareae. Juel (4) 
records thirty-five species in various tribes ; Kolreuter (6) records 
twenty-three species of which thirteen are Centaureae , and other authors 
have recorded only a few more. 
The method used in the present investigation was to touch the anther 
tube gently with a needle and observe the result with a watchmaker’s 
[Annals of Botany, Vol. XXXI. No. CXXII. April, 1917.] 
T 
