203 
antero-posterior one: thus 12 cm. 0.8; 1 cm. 0.65, The basal 
part of the branch from which the hook arises also thickens 
considerably, but the distal portion gener- 
ally remains thin. Hence the hook often 
assumes the misleading appearancesimul- 
ating the stalked hook of Artabotrys (shown 
in Fig. 1), where the dotted line shows the 
point of origin of the sessile hook. This 
thickening of the basal portion of the 
branch only takes place, when the contact 
is prolonged, and the hook is subjected to 
considerable strain, whilst, in correlation 
with the change in function to a supporting 
organ of the basal portion below the hooks, 
the distal portion may bear but few, or no, 
leaves or branches. With unattached hooks, the branch does 
not perceptibly differ above and below the hook. 
The following experiments, along with those already mentioned, 
shew, that an injury may act as a slight stimulus, that a 
rough surface acts as a stronger stimulus, than a smooth one, 
and causes the surface of the hook in contact to become brown, 
roughened, and corky, that the greater the area of surface in 
contact, the more marked is the response produced, but that, 
the most powerful factor in producing the increase in thickness , 
is the strain, to which the hook is subjected. 
Roucheria Grifithiana. Each datum is the average of 5, 6, or 
10 experiments. 
Meenas saerct by. 8? |S 
(2.) Untouched hooks. vey 0 a ke 
(4.) Tightly fitting wooden plug inserted 1/s kilo’s ah ee kl 3 
c.) V i ing ides also 2 : = 
(c.) V shaped piece of wood 5 grm., pressing on si : 15° = 150.195Ja 
(4) Glass rod, tightly fitting 
S—S A—P 8—S -- 
Hooks bound tightly round back with rough bast ot . pe ; nag rd 
ees ” w ” v n loops of Cu wire - 2193 . 
@) Loops of twine, 0.29 mm. weight, attached 143. py o : “ 
(4.) Similar but untouched hooks a pax 
() Epidermis removed on concave surface, injury superficial 17 re 
3 
‘) Hook supporting loose coil of Cu wire weighing 1.5 grm. 220. 
