THE LORANTHACE^ OF CEYLON. Ill 



subsequently entered. In addition to this entry by pressure, woodcut 2, already 

 referred to, shows, I tliink, quite clearly that each cell penetrates a cork-cell, and that 

 the cell-wall through which it has to pass completely disappears, and is not merely 

 pushed inward and ultimately ruptured. In this method of penetration partly by 

 pressure, partly by solution, these surface-cells of the sucker present a close parallel with 

 those of the baustoria of Cuscuta, Tourn.*. 



Returning to the question from which this discussion arose, contact has been shown 

 to influence the outgrowth of the " root-end " of the head of the hypocotyl, and probably 

 also the growth and nature of the papillate cells of the head ; but, on the other hand, 

 the swelling of the head is not promoted by mere contact — does not take place when its 

 distal surface comes in contact w^ith an inert body, as glass or tinfoil. It seems, therefore, 

 that this swelling is the result of a stimulus in some way due to the penetration of the 

 hairs into the host, and possibly to be likened to the later hypertrophy of the host-stem 

 itself at the place Avherc the parasite sits. 



Finally, with reference to the action of contact and pressure, it was found that 

 whereas a " suctorial disc " of a rapidly elongating hypocotyl, on reaching a branch, very 

 quickly applied itself closely to that branch, it, on reaching an inert body, such as 

 tinfoil or glass, slid along that surface, leaving a resinous track, and sooner or later 

 curved completely aw^ay, even though in so doing the head was brought directly toward 

 the light. It seemed at first that this was the result of contact, and in the sense that 

 ** every stress, every strain produces an accelerating or inhibitory effect on growth "f, 

 contact, clearly, does produce an effect ; whether, however, the edge of the hypocotyl is 

 sensitive to contact in the narrower sense in which root-tips and tendrils, etc., arc said to 

 be, is not decided by the mere fact that, generally speaking, when the head reaches a 

 branch it remains there, but when it comes in contact with inert bodies it curves away. 

 Such a view w^ould necessitate a belief that the hypocotyl possessed some selective 

 power in determining its host, a supposition which is unnecessary. Pfeffer has demon- 

 strated that tendrils, which of course possess in a high degree contact-irritabiKty, do 

 not respond when brought into contact with wet gelatine — that this sul)stance does 

 not call forth contact-irritability. Pierce has recently used this method in investigating 

 the presence or absence of contact-irritabiUty in the stem of CuscutaX. It was applied 

 in the case of the suctorial discs of Loranthus lonicei^oides. Seedlings were so placed 

 that their hypocotyls were bending downward on to glass plates covered with thin 

 gelatine, over whose surface water was continually drawn by means of strips of 

 blotting-paper. The head soon reached the gelatine and quickly curved away. So that, 

 usin"" the contact-irritability of tendrils as a standard, the curvature of the head away 

 from the surface of the gelatine shows that there is no need to suppose that the head is 

 possessed of contact-irritability. 



An examination of the various forces which may contribute to the opposite results of 



* Pierce, ' Ann. of Botany,' viii. lyoi, p. 55, etc. 

 t Pfeffer, ' Plianzenphysiologie, Bd. ii. p. 151. 

 + Pierce, loc. cit. p. (i5. 



