James Small. 253 
THE ORIGIN AND DEVELOPMENT OF THE 
COMPOSITE. 
By James Small, M.Sc. (Lond.), Ph.C. 
Chapter III. 
IRRITABILITY OF THE POLLEN-PRESENTATION MECHANISM. 
I T is probable that physiological differentiation precedes morpho¬ 
logical differentiation in the history of a species and causal 
morphology must have a physiological basis for its sound study. 
Preliminary investigations are, therefore, in progress on the 
physiology of the Composite, and the present chapter deals 
with one of the most striking effects of physiological differentiation 
in the family, the irritability of the styles and stamens. The 
history of our knowledge of irritability is summarised briefly ; the 
known cases of irritability are given, their physiology discussed, 
and the phylogenetic significance of the phenomenon in the 
Compositae is considered in the light of the previous phyletic 
suggestions made in Chapter II. 
A. History. 
Styles :—Our knowledge of irritable styles in the Compositae 
is of comparatively recent origin. The first reference to the 
movement of the style when touched is that in an unsigned article 
(30, 1815) by Ker on Arctotis aspera. He also records the same 
phenomenon in A. aureola (=A. aspera , L.), and suggests that 
“ the style .... seems to consist of a substance resembling 
elastic gum (Caoutchouc).” 
Brown (4) refers only to Ker, and Cassini (7) records that he 
observed the phenomenon in “quelques arctotid^es,” but gives no 
details. Muller (43) and Knuth (34) give Arctotis aspera u and 
other species.” Minden (42) records Arctotis aspera and A. 
calendulacea (= Cryptostemma caleudulacea, R.Br.) as irritable, 
and discusses the physiology of the process (see below, Section D). 
Juel (28) extends the phenomenon to Arctotis stoechadi folia, and 
the writer has published a preliminary, illustrated account (47) of 
the phenomenon in A. aspera. 
In other families the phenomenon of movement of the style 
or stigma when touched seems to have been known at a much 
earlier period, as the facts were apparently common knowledge 
when Kurt Sprengel (52, 1817) wrote of the irritable stigmas of 
