222 THE BIOLOGY OF FLOWERING PLANTS 



in the temperate zones it is poorly represented. A few 

 species occur in Europe, and one of these, Viscum album, 

 the mistletoe, reaches England. We may take this most 

 familiar of all parasites as a representative of the family. 

 The white pseudo-berries contain each one seed which 



is deposited on the branches 

 of trees, either after passing 

 the alimentary canal of a bird 

 like the missel-thrush, or, 

 more usually, from being 

 rubbed off against the bark as 

 the bird endeavours to free its 

 beak from the viscid pulp of 

 the fruit wall. This slime, 

 used as bird lime, fixes the 

 seed to the branch till rising 

 temperature and longer illumi- 

 nation permit germination to 

 take place, about the begin- 

 ning of May in central Europe. 

 The seed germinates on any 

 substratum, even on a sheet 

 of glass, and it can be made 

 Fig. 24.— Attachment of para- to germinate in winter if the 

 sites: i cross-section of host temperature be high enough, 



root with clasping root of , . r • r • 1 -ii 



Osyris alba; the splayed-out and if artificial illumination 

 end of the sucker has been j^g employed, for it germi- 

 enclosed by secondary thick- 1 • i- 1 /tt • • 1 



ening ; 2, section of tuber of nates only in light (Heinricher, 



191 6). The base of the 

 hypocotyl — no radicle is formed 

 — leaves the seed coat. For 

 a short time, as Heinricher 

 (191 6) has shown, it is negatively geotropic, but it soon 

 loses its power of reacting to gravity and becomes nega- 

 tively phototropic, so that its free tip curves round and 

 grows towards the branch on which it lies ; the tip becomes 

 pressed to the surface and flattens out into an adhesive 

 disc. From the middle of this a peg-like sucker grows out 



Balanophora globosa pene- 

 trated by tissue from the host 

 root. I, slightly magnified; 

 2 = § nat. size. (After Solms- 

 Laubach.) 



