THE LORANTllACE.E OF CEYLOX. 100 



Tn the dark, where, as has been mentioned, the rate of growth of the hypocotyl of 

 Loranthns loniceroidesh much less tlian in light, the ho^'id docs not assume aconicjil form, 

 hut, by the outgrowth of its originally flat distal surface, becomes almost spherical, or the 

 white projection may grow out beyond the general surface of the disc. In L. neelgher- 

 rensis a similar white projection from the free end of the hypocotyl often, even when the 

 latter is free and the seedling is grown in the light, reaches a length of several millimetres. 

 In this species such an outgrowth, about 2 mm. in length, pointed in one case vertically 

 upward, thus seeming not only to be agcotropic, but also to have no reactivity to light, 

 since after the outgrowth had commenced the seedling was removed from the dark and 

 so placed that it received light from one side only. 



The interest of the question lies in the fact that the aerial roots which develop later 

 are in a high degree negatively heliotropic, turning back on themselves on reaching the 

 free ends of branches along which they grow, and generally seeking the under-sides of 

 these branches. 



V. — Effect of Contact on the Hypocotyl and on its Suctorial Disc. 



In the preceding section the relative influences of nutation and negative heliotropism 

 on the ultimate position of the hypocotyl were discussed. 



I endeavoured further to ascertain what other irritabilities the hypocotyl possessed — 

 whether contact or pressure produced any curvature-movement. I found that tlie 

 general surface of the hypocotyl was not irritable to contact : that when, for example, 

 threads bearing small weights were hung over the hypocotyl no effect or curvature was 

 produced. Hypocotyls of L. loniceroides growing in the dark, in which the curvature 

 was slight, were also tested by means of these threads, and they also showed no contact- 

 curvature. 



I next sought to ascertain whether the suctorial disc (head of sucker) was affected by 

 contact after the manner of roots*. Small squares of various objects, such as paper, 

 sand-paper, and bark, were afExed by pressing them gently but firmly into the resin-drop 

 which covers the head of the sucker, so that they stuck on obliquely. In no case did 

 any curvature result, so that neither the edge of the hypocotyl nor its general surface 

 responds by curvature to contact. 



Nevertheless the minute pieces of paper, etc., do produce an effect on the growth of 

 the free surface (root-surface) of the sucker, llepeatedly, as the result of the contact- 

 stimulus set up by these small objects, the " root-end *' of the hypocotyl, i. e. the free 

 distal surface, grew out not symmetrically, but in the region of the affixed body. In 

 other words, contact has an influence in bringing about the development of tluj 

 projections similar to those referred to in the preceding section. This was corroborated 

 in several ways. 



Firstly, on four or live occasions small flies were observed to be caught on the viscid 

 drop of resin (which covers the distal surface of the suctorial disc). These flies died and 

 gradually turned brown, and irregular projections of the free surface grew out in their 

 direction. 



* Cf. Daxwin, ' Power of Movement in Plants,' p. 125, etc. 



q2 



