104 MR. F. W. KEEBLE ON 



IV. — The Curvature and Growth or the Hypocottl of various 



Species of Loranths. 



Since the time of Dutrochet it has been known that the hypocotjd of Viscum album is 

 negatively helio tropic *. De Candolle sums up the case thus : — 



" If germinating seeds of Viscum album be placed inside a room close to the window, 

 the hypocotyls direct themselves horizontally away from the window ; if they be placed 

 just outside the windoAV, the hyj)ocotyls turn to the glass as if to pierce it, in making 

 for the dark " f . Duhamel % also long ago proved that '* gravity " has no directive 

 influence on the hypocotyl of Viscum album. 



Wiesner has somewhat recently shown that the seedlings of Viscum album will 

 not grow in constant darkness, light being necessary for their phototonic condition §. 

 This fact was verified by Guerin in 1892 ||. 



I may say at once that, although it was almost superfluous, the absence of gcotropism 

 and the existence of negative heliotropism were confirmed by me in the hypocotyls of 

 two species of Loranlhus, — L. loniceroides and L. neelgherrensis. In the cases of 

 Ij. cuneatus, Zu lonffiflorus, L. capilellatus, and Notothixos floccosus also, observations 

 made on the direction of curvature during germination experiments showed that 

 geotropism plays no part, and negative heliotropism a very great part, in eflecting the 

 curvature of the growing hypocotyl. 



So far, the analogy with Viscum is complete ; but with respect to growth in the dark 

 there is a striking difference. I find that tlie members of the genus Loranthus differ 

 among themselves, and from Viscum, in this respect. 



Bipe seeds of L. loniceroides and L. neelgherrensis were stuck on the branches of a 

 species of Limonia growing in a pot, which was then placed in a dark room. At the 

 end of two weeks the plants were examined, and gave results from which the following 

 conclusions are drawn : — 



Loranthus loniceroides stands midway between Viscum album and other species of 

 Loranthus. The hypocotyls of this species grow in the dark, but very slowly, com- 

 pared with similar hypocotyls exposed to the light. 



In L. neelgherrensis, the growth and curvature of the hypocotyl in the dark is great ; 

 indeed, in one case, to be discussed in another connection later, the growth was 

 sufficient to bring the head of the hypocotyl in contact with the branch on which it was 

 stuck, and enable the " primary root " to grow from the hypocotyl into the host in the 

 form, as microscopic examination showed, of a wedge-shaped mass of cells. 



This is not surprising, so far as the outgrow^th of the " root " from the head of the 

 hypocotyl is concerned, for, as I shall show, darkness seems to favour this outgrowth. 

 The surprising part of the affair is the ability — in the absence of light — of the hypo- 



* Dutrochet, ' Recherches anatomiques,' 1 vol. in 8vo. Paris, 1824. 



t De Candolle, ' Physiologie Vegetale,' vol. iii. p. 1410. 



+ Duhamel, ' Physiologie des Arbres,' 1758, vol. ii. p. 137. 



§ Wiesner, in Bot. Zeit. 1878, vol. i. p. 43. 



II Ch. Guerin, "L'Histoire naturelle du Gui," Bull. Soc. Linn. Nonnandie, ser. iv vol. vi. 1892. 



