io6 Chapters in Modern Botany CHAP. 



thoughts to the terrestrial species of Utricularia (p. 31). 

 Few botanists imagine that this strange and local plant may 

 be cultivated ; it grows well under cherry laurels (" common 

 bay," Cerasus laurocerasus) in the shrubberies of the 

 Edinburgh Botanic Garden, and hence at least suggests the 

 possibility of its introduction elsewhere. 



Broom-rapes. In our search for the toothwort we may 

 perhaps find one of the broom-rapes (Orobanche\ which 

 grow parasitically on the roots of thyme, scabious, and other 

 common plants. As in Lathrsea, there is no chlorophyll ; 

 but the union between parasite and host is much more inti- 

 mate, so much so indeed that it is difficult to separate them, 

 or to tell where the tissues of the parasite end and those of 

 the host begin. The seedling of the broom -rape and 

 related parasites is very remarkable ; it bears no trace of 

 cotyledons, but is a delicate thread-like structure, one end 

 of which is hidden by the remains of the seed, while the 

 other grows in search of roots to which to fix itself. If 

 these be not soon found, the seedling shrivels and dies, for 

 it seems quite unable to absorb food from the soil. But if a 

 suitable host be found, the seedling becomes ultimately 

 united with it, thickening into a knotted tuber-like structure, 

 from which the flower-bearing stem with its brown useless 

 leaves will afterwards rise above the ground. 



Thus from the non-parasitic toad-flax and its allies, 

 which we shall come to know better as the natural order 

 Scrophulariacece, commonly gay flowered and free growing, 

 often indeed mischievous as weeds, we have a regular 

 gradation through cow-wheat and Euphrasy, lousewort and 

 Bartsia, to full parasites like toothwort and broom-rape. For 

 still further modified allies of the broom-rapes (Orobanche) 

 we must travel abroad, especially to tropical countries, 

 where there are many strange plants (Balanophoreas) of 

 similar habit but strangely crowded and reduced flowers. 



