James Small. 
256 
is right in his explanation that the retraction is due to the elasticity 
of the filaments, and Gray is right when he controverts Meehan on 
the elongation of the filaments being due to a pressure exerted by 
the style. The proximate cause of the elongation of the filaments 
seems to be an increase in turgor (see Section D). 
Irritable stamens in other families were unknown to the earlier 
botanists, 1 and according to Goeppert (12) the first to record the 
movement in Berberis was Linne (1775). Goeppert gives a good 
historical account up to his date (1828). Smith (51) was the first 
to locate a motor region in Berberis. Kurt Sprengel (52) recorded 
staminal movements in Parnassia, Cacti, etc.; Kitchener (33) 
recorded a gradual contraction and contortion of the filaments in 
Achimenes ; Bessey (1), Meehan (39) and Halsted (17) made various 
observations on the movements of the stamens in Portulaca spp. 
Halsted also recorded experiments on Berberis (19-20). Tomney 
(53) records about 50 species of Opuntia which show irritability of 
the stamens, while Pfeffer (46) records the phenomenon in Mahonia, 
Heliantliemnm and other Cistaceee, Mesembryantheniuni. Opuntia, 
Cereus, Spanuannia and certain Tiliaceae and Portulacaceae. 
B. Irritability of the Styles. 
Outside the Compositae the only genus recorded as having a 
style which moves towards the touch is Glossostigina (46), but the 
stigmatic lobes are sensitive and close when touched in various 
other genera such as Mimulus (29, 33, 44, 46, 52), Martynia 
(Martyniaceae) (21, 44, 46, 52), Strobilanthes (= Gold/ussia, 
Acanthaceae) (44, 46) and Bignonia (Bignoniaceae) (46). To these 
may be added Torenia. The stigma of Torenia Fournieri in India 
shows the same form of irritability as Mimulus, but other species, 
such as Torenia vagans, are not sensitive, nor is T. Fournieri when 
grown under glass in this country. 2 
In the Compositae the phenomenon as at present known is 
confined to the Arctotideae. It occurs in Arctotis aspera (30, 42,47), 
A. stoechadifolia\{ 28) and Cryptostemma calendulacea { 28,42). To 
these may be added the Gazania splendens of gardens. Ker (30) 
gives Arctotis aureola, Ker Gawl, also, but this is synonymous with 
A. aspera, L. The phenomenon in Arctotis aspera has been 
described in detail by the writer elsewhere (47), but a brief resume 
is given below in order to facilitate reference. 
1 There is a considerable literature dealing with the stamens of Berberis , 
but most of it is irrelevant in the present argument. 
3 For this information about Torenia I am indebted to the Director of the 
Royal Botanic Gardens, Kew. 
