104 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. j 



long annular ducts — and (to me) sj)iral ducts with ; 

 the fibre unrollable, however, as far as I have been 

 able to detect — will be found. I may also remark 

 that the long pleurenchymatous cells surrounding | 

 the first-foi'med vascvilar bundles are carried along i 

 with the latter to the centre of the plant, around , 

 the pith of which they may be found, a circumstance i 

 somewhat analogous to that stated by Decaisne to ' 

 take place in ^fenisperinacece"* \ 



The most striking characteristic of the plant, 

 however, is its parasitism. It occurs in Britain j 

 most commonly on the apple, crab, hawthorn, and | 

 certain poplars ; but it is frequently found on many 

 other trees both indigenous and introduced. It is 

 very unusual on the oak, pear, beech, birch, bird- I 

 cherry, wild cherry, blackthorn (or on any of the | 

 cultivated cherry or plum trees), hornbeam, elder, ; 

 holly, dogwood, boxtree, Lombardy poplar, sweet 

 chestnut, or laurel. There are undoubtedly several 

 causes that may affect such relative frequency, as, 

 for instance, the more jDlentiful diffusion of its 

 seeds on trees frequented by the birds that eat its i 

 berries, or the existence of certain peculiarities of 

 bark that prevent it from gaining a hold. The [ 

 tannin of the oak may perhaps be injurious to the * 

 germinating rootlets, and yet not altogether a pro- 

 tection against the x^arasite. It is difficult to under- \ 

 stand why it should be so common on the apple ; 

 and so rare on the pear — even when they grow ! 

 together in orchards — except we assume that there : 

 is some difference in the structure of the bark or 

 in its chemical composition that hinders the ger- 

 minating mistletoe from obtaining a settlement. 



The young plant insinuates its radicle into the \ 

 bark of the victim tree, and it ahvays pushes j 

 forward towards the centre of the branch till it 

 reaches the cambium layer, when it ceases to pene- 

 trate further. This root is thus at right angles to ' 

 the surface of the wood; but it gives off several ' 



* Annals of Nat. Hist, ix, 8i. ] 



