774 REPORT—1904. 
element we should expect the stimulus to increase as the angle increased—from 
135° to nearly 180°—which is not the case. From my point of view we can dimly 
understand why 135° should be the position of maximum stimulation. It would 
he the result of a compromise, being a position in which the combined pressure on 
both lateral and apical walls was as high as possible'—a mean, in fact, between 
full pressure on the lateral walls (as in the horizontal position) and full pressure 
on the apical walls (as in the vertical position). 
If some such theory is not adopted we must imagine with Haberlandt that the 
difference between positions i. and ii, depends on the weight of the statoliths in i. 
being on the basal half of the lateral wall, and on the apical half in ii. It seems 
to me that the difference of sensitiveness in the two regions would have to be very 
great, considering that in the horizontal position, in which the gravistimulus is 
less than in position ii., the full pressure of a considerable fraction of the total 
starch acts on the supposed extra-sensitive region of the cell-wall. 
But when all has been said there remains a difficulty with which I do not 
Fria. 3. 
i, ii. 
know how to deal. It is clear that, according to either theory, the critical 
position should be the horizontal, and that as the organ is moved further and 
further from the normal (in successive experiments) the geotropic reaction ought 
to increase decidedly as the horizontal is passed, and this is not the case, 
Diageotropism. 
The diagram, fig. 2, will serve to represent a diageotropie organ in stable 
equilibrium. In spite of the fact that it is at rest in the horizontal position, we must 
assume that the tangential (horizontal) walls of the endodermis are sensitive to 
the pressure of the statoplasts. For when the organ is placed obliquely it has the 
power of returning, by curvature, to the horizontal; and this requires that the. 
plant shall distinguish up from down. If its apex is above the horizon it must 
curve downwards, 7.c., towards that side on which the statoplasts rest on the 
external walls of the endoderm cells, and vice versa if the apex is below the 
horizon. But what signal tells the plant that it isnot horizontal? This can only 
he effected by the statoplasts pressing on the basal or apical walls, as in fig. 3. 
The difficulty is increased by the fact that when a diageotropic organ is fixed 
vertically, the apex being up or down,’ no curvature follows. This, according to 
' The fact that at angles above 135° the stimulus remains greater than when the 
organ is horizontal seems to point to the conclusion that the share of the end 
wall in graviperception is relatively great. 
* Czapek (98, p. 243). Noll (92, p. 37), had foreseen on theoretical grounds that 
this would prove to be the case. See also Noll (00, p. 473). 
