OF BUCK LEY A QTJADRIALA, B. ET IT. 33 



In Fig. 12. b the course of the vessels of the neck is shown 

 in longitudinal section. The vessels in this part are more or less 

 stretched, so that they are longer than those of the axial part. 

 They have transverse walls at both ends (Fig. 13). 



Generally, as the vascular strand of the old haustorium sur- 

 passes in growth the woody part of the mother-root, the vessels 

 in the neck diverge towards the bottom of the haustorium. 



As to the cortical part of the neck, it will not be worth 

 while to say more than that it has the same structure as that 

 of the main part of the haustorium, consisting entirely of paren- 

 chymatous cells of equal size and arrangement, but with no 

 striated bands among them (Fig. 12. a). 



The study of the secondary growth of haustorium makes 

 it very easy for us to understand its outer form, which is mainly 

 determined by the form and arrangement of the constituent tissues. 

 In the young stage the axial part is comparatively smaller than 

 the cortical part, so that it is the latter that chiefly determines 

 the form at that stage ; for instance, the development of the 

 attaching-fold determines the form, according to the degree of its 

 thickness and size. 



The length of the neck is also a factor in determining the 

 form of the young haustorium : the shape of the latter is that 

 of a long cone if the neck be moderately long. In one case I 

 have found a conical-shaped haustorium 3 years old, and 7 mm. 

 in height, of which 3,5 mm. formed the length of the neck — the 



ment of vessels is not yet completed, the part of the so-called neck is only with difficulty 

 distinguishable. In Osyris judging from the figure given by Soi.ms-Laubach (loc. cit. Taf. 

 XXXII, Fig. 7), one pair of arch-shaped strands of vessels composing the axial part of the 

 haustorium seems to start directly from the sides of the wood of the mother-roots. 



