of Masdevallia muscosa , Rckb. f 249 
but rather vertically downwards to the neighbourhood of 
the vascular bundles and then travels in or near them to the 
neck. In the second experiment, in which the bundles were 
cut, no stimulus was transmitted. 
(3) A further experiment was made on another flower. 
A transverse cut across the blade was made from below 
(Fig. 1 8 , B) so as to sever the vascular bundles ; the cut was not 
continued upwards and the crest remained intact. On stimu- 
lating the crest at a point on the distal side of the cut it 
was found that a contraction occurred only after repeating 
the stimulus and then was somewhat sluggish. The stimulus 
here had to travel obliquely downwards and forwards to reach 
the uncut part of the vascular bundles ; the slowness of the 
transmission here being perhaps due to the unaccustomed 
oblique route to be traversed in reaching the bundle, whilst 
normally the stimulus would make its way directly to the 
vascular bundles, i. e. vertically downwards, and be rapidly 
transmitted to the contractile region. 
In Fig. 13 the xylem is seen to be accompanied by a con- 
spicuous sheath of thin-walled parenchyma with copious tannin 
content (see p. 241). It seems to me quite possible that the 
stimulus travels by this sheath, although I know very well that 
the experiments above recorded do not show whether the 
stimulus travels by this sheath or by some other element of 
the bundle. All they indicate is that it passes in the im- 
mediate vicinity of the bundle, not necessarily as a wave of 
disturbance in the tracheides. In a former paper 1 I have tried 
to show for the case of the stigmas of Martynia , and others, 
that it is not the string of tracheides which conducts the 
stimulus, but the general parenchyma. In the case of Masde- 
vallia , I believe the parenchyma, which conducts the stimulus, 
to be consolidated with the vascular bundle, constituting the 
tannin-containing sheath referred to. In Martynia we have to 
deal with a more generalised case, the vascular and stimulus- 
conducting tissues not being approximated. The conducting 
1 F. W. Oliver, Ueber Fortleitung d. Reizes bei reizbaren Narben, in Ber. d. 
dent. bot. Ges. 1887, p. 162. 
