of Masdevallia muscosa , RcJib. f. 247 
This still retains its primitive function in P. Woolsii and in 
a few other species. In many species of Pterostylis it has 
become gradually modified for purposes of attraction by the 
appendaging and fimbriating it has undergone. In the relaxed 
position of the labellum this emergence occupies a prominent 
position in the mouth of the flower. That in this further 
adaptation the emergence has entirely lost its supposed 
primitive function I am unable to say; a few experiments 
on living material would easily enough decide 1 . In some 
species (P. Woolsii ) the change of function has not occurred. 
Though analogous in function, the emergence in these 
two genera has a quite different insertion. In M asdevallia 
it is inserted at the proximal end of the band-like neck, and 
is directed forwards ; in Pterostylis at the distal end, and 
directed backwards (compare Figs. 4 and 16). Further, in the 
former it is entirely non-vascular, in the latter — in some 
cases, at any rate, from an inspection of dry material — 
it is supplied with a string of tracheides. 
Transmission of stimulus. — As regards the nature of the 
change occurring in the cells which bring about the con- 
traction, i. e. those of the upper side of the neck, there seems 
no reason that it should differ from that in the contractile 
half of a pulvinus of Mimosa. It will be remembered that in 
this case the stimulus causes a loss in turgidity of the cells 
of one-half, so that these no longer offer any antagonism to 
the still turgid cells of the other half : hence the movement. 
As in the pulvinus of Mimosa , so in Masdevallia , numerous 
small intercellular spaces are present between the corners 
of the thin-walled cells of the upper half of the neck, and 
the phenomenon of contraction is no doubt due to a sudden 
diminution of turgidity in this part, accompanied by an 
outflow of water into the intercellular spaces. Whether there 
be a definite act of contraction by the protoplasm which 
causes an out-passage of water by filtration under pressure 
(Vines), or whether there be a sudden diminution of osmoti- 
1 Fitzgerald gives no observations as to the function of the emergence. For the 
suggestions here made I am alone responsible. 
