112 ME. F. W. KEEBLE ON 



impact with bark and with inert bodies respectively shows, I think, that this behaviour 

 may be explained without the help of contact-irritabiUty on the part of the head or edge 

 of the sucker. 



There are in both cases various " forces " tending to keep the sucker in its place 

 on the branch, and others tending to carry it away. Among the former are negative 

 heUotropism, the resin on the free surface, rapid growth of papillae into the host 

 inducing swelling of the sucker especially at its edges, whereby it may be imagined to act 

 somewhat after the fashion of a surgeon's " cup." On the other band, tending to the 

 removal of the head of the hypocotyl, is the nutatory growth which, acting favourably at 

 one time, will act unfavourably at others ; and the pressure-effect, whereby the hypocotyl 

 tends to take the line of least resistance. In the case of hypocotyls attaching to the 

 branch, the factors favouring adhesion outweigh those tending toward removal of the 

 head ; but not always, and therein lies confirmation of this view. It has already been 

 remarked that hypocotyls whose heads come very soon in contact with a branch are 

 carried completely away from the branch into which other heads of hypocotyls, whose 

 curvature is more complete, are growing quite normally. In other extremes, also, the 

 same thing occurs. Old hypocotyls which are nutating in small irregular circles may 

 come in contact with a favourable branch, and yet, owing probably to failure of resin and 

 hairs, be carried away by the continuation of the nutation. 



This curving away from the surface is the normal course of affairs when the host is 

 some hard inert body, such as glass or tinfoil, for the nutation tends toward removal, and 

 fixation is not aided by an ingrowth of the surface-cells, nor by the growth of the edges 

 of the disc (and this latter seems to have an indirect effect as well, inasmuch as the resin 

 is not pressed well into the surface of the host and does not set firmly). 



To briefly sum up this section : — absence of Hght tends markedly in Loranthus lonice- 

 roides to inhibit growth of hypocotyl, less so in such species as L. neelgherrensis ; absence 

 of light promotes the outgrowth of the root-end of the hypocotyl, i, e. root-formation. 



The general surface of the hypocotyl does not respond to contact. Contact, however, 

 favours the outgrowth of the root. The root, in growing out, exerts considerable pressure 

 — sufficient in some cases even to split the bark of the host-branch. 



The hypocotyl curves away from inert bodies, and even from its natural host when 

 reached at unfavourable times. This curving away is not the result of contact-irrita- 

 bility, but represents the direction of the resultant of opposing " forces," viz., on the one 

 side nutation and pressure-effect (line of least resistance), on the other negative heUo- 

 tropism, adhesive power of resin and of ingrowing papillae, and growth of the rim of the 

 suctorial disc. 



