James Small. 
2 72 
and Martynia the transmission of the stimulus was completely 
independent of the vascular bundle, and that the presence of a well 
developed system of intercellular spaces confirmed Pfeffer’s theory 
of the extrusion of water and loss of turgor as the cause of the 
movement. Chauveaud (8) controverts Pfeffer and returns to a 
position similar to that of Cohn. Minden (42), however, considers 
that the style of Arctotis shows analogies in structure and 
movement with those described by Pfeffer in the stamens of the 
Cynarese. The marked effect of the meteorological conditions 
on the movement of the styles (47) and stamens (49) is 
another piece of confirmatory evidence. The fact recorded by 
Harger (21), that if no pollen is placed between the stigmatic 
lobes of Martynia they soon re-open but with pollen this never 
occurs, also shows that the movement is no mere mechanical one. 
Most of those who have described the tactile hairs, especially 
Haberlandt (15), consider them to be organs of perception, but 
Halsted (18) has recorded a movement in at least two species in 
which no tactile hairs are present. Many of the species given in 
Table VIII also show no tactile hairs and Linsbauer (37) regards 
these hairs when present as stimulators or stimulus-transmitters 
rather than organs of perception. 
It may be considered proved that a loss of turgor when the 
filament or style is touched is the cause of the movement, and 
Haberlandt states that “ it is not known whether the fall of turgor 
depends upon a sudden diminution of the osmotic strength of the 
cell-sap, caused by the external stimulus, or whether the latter 
brings about an increase of the permeability of the ectoplast 
towards the osmotically effective constituents of the cell.” If we 
consider that the cell-sap has a much more stable composition 
than the ectoplast, and that the latter is protoplasmic and there¬ 
fore in a condition of unstable equilibrim, it is not difficult to see 
which is the more likely to be affected by a sudden change on 
being touched. Dr. F. F. Blackman in a recent lecture 
(London, 1913) suggested that the irritability of the stamens in 
the Cynarese might be due to permeability changes similar to those 
in the pulvini of Mimosa and Phaseolus. The writer (50) has 
recently shown that the geotropic sensitiveness of the root is due to 
permeability changes giving a differential loss of turgor and con¬ 
sequent movement. The difference in the time relations of the 
movement in the root and the filaments is to be explained by the 
state of tension of the latter and their relative slimness. In those 
cases where tactile hairs are absent the same deformation of the 
sensitive protoplasm may occur in the epidermal cells as probably 
