237 
surfaces of the cells a thick brown cuticular layer. Where this 
has taken place the root can no longer respond to contact by 
either curving or producing root hairs. Hence in the older roots 
it is only the region, extending a centimetre or two backwards 
from the growing point, which is sensitive to contact. If the 
root-tendrils develop in damp air and in darkness, the forma- 
tion of the cuticular exodermal layer is retarded or inhibited, 
and the root remains longer sensitive in contact. These two 
phenomena are however not necessarily interdependent but may 
be only accidentally correlated. 3 
For the formation of root hairs on the root-tendrils moisture 
is essential, darkness and contact accelerating, and light and dryness 
retarding it. Thus if the root-tendrils are caused to grow into 
glass tubes (a) open and dry, (4) filled with moist air, (c) dry 
and in darkness (¢), in darkness and moist air; in (a) root 
hairs form only on the sides in contact, in (4) and (c) they 
form first on the sides in contact but later more or less over 
the entire surface of the root; whilst in (d) they form most 
rapidly of all and on all surfaces of the root. 
If all other directive agencies are removed the root-tendrils 
are seen to be faintly geotropic and weakly aheliotropic '), and 
they also possess fairly strong aerotropism or oxytropism ’), i.e. 
if grown into closed tubes containing a large amount of C 0, and 
relatively little oxygen, they may bend upwards and grow out 
again. If the root tendrils are allowed to grow, whilst quite young, 
into long dark tubes filled with moist air, they grow almost in- 
definitely in length (in one case more than 3 feet), and if they 
then reach the ground, they may strike root, branch, and develop 
a great abundance of root hairs, and thus finally be conver- 
ted into nutritive roots, “Nahrwurzeln”. In one case, some 
structures and 
but the 
bilities. 
readily 
1) The leafy outgrowths from the hooks of Artabotrys are stem 
shew the same physiological properties that ao ordinary branch does, 
hooks in all cases appear to be destitute of heliotropic and geotropic irrita 
Many tendrils however appear to possess a slight heliotropic irritability, 
Overcome by the stimulus of contact. 
2) Ewart. Trans. Liverpool Biol. Soc. Vol. 
bot. Ges. 1884. IL. p. 160. 
X. 1896. p. 190; Molisch. Ber. d. 
