260 The Plant World. 



ment is produced by a sharp thrust a definite, rapid response 

 follows. 



If such a thrust is applied so as to bend the lip chiefly in a 

 transverse zone near the base, as indicated in a, Figures 2 and 

 3, the consequent bending will be confined to that zone, and the 

 curvature of the lip, seen in profile, will be represented in Fig- 

 ure 4. If, however, the thrust is applied to the apex of the lip 

 so as to bend it in a transverse zone near the apex, (Fig. 2 b) the 

 curvature is similarly confined to this zone. The resulting re- 

 sponse is as shown in Figure 5. Either lateral edge of the lip 

 behaves similarly by appropriately confining the thrust, e. g., 

 to the zone c, Figure 2. * A complete curvature of the lower lip 

 so as to oppose itself against the apper (Figure 1) results only 

 from such displacement as directly affects all the cells of the mot- 

 ile parenchyma. The above is equally true of the upper lip 

 also, but there is no transmission of stimulus from one to another, 

 Diplacus agreeing in this regard with Mimidiis lutciis (Oliver /, c). 



Further, if the pressure is not applied symetrically with 

 reference to the median plane, by applying pressure with a very 

 slender, lead-tipped glass rod at, say, a point indicated by d, 

 Figure 2, the movement is greater on the side receiving the 

 greater pressure. The one lip thus takes an oblique position 

 with reference to the other, (Figure 2, d.). 



The most obvious inference to be drawn is, that the stimu- 

 lus is not only not transmitted from one lip to the other, but that 

 it is not transmitted at all. The alternate inference, that it is 

 transmitted weakly for a short distance only, has logical value 

 as a possibility and is, indeed, suggested by the fact that the 

 cognate forms which have been mentioned fall, according to the 

 results of the workers above mentioned, into a series of decreasing 

 sensitiveness with Diplacus the lowest member. 



Forward displacement, that is, pressure on the outer face 

 of the stigma-lip (Figure 3, c). Because of the curling back of 

 the edges of the lip, it is important to avoid bending them in 

 applying pressure to the back. The bead-tipped glass rod was 

 successfully used for the purpose. The following experiments 

 are typical. 



*I have found this account true of Mimulus luteus. 



