NUTRITION 89 



but differing strikingly from the otiier members of the 

 family in habit and habits. They are leafless twiners, yellow, 

 orange, or even sometimes claret-red, in color, with very 

 little if any chlorophyll. At frequent intervals their stems 

 and branches form close coils around their hosts,* and 

 from the inner surfaces of these coils haustoria grow into 

 the tissues of the hosts. The haustoria have well-developed 

 vascular bundles, the xylem and phloem of which are united, 

 cell to cell, with the xylem and phloem of the adjacent vas- 

 cular bundles in the host, thus perfectly connecting, in host 

 and parasite, those tissues which conduct aqueous solutions 

 of mineral salts and of elaborated foods respectively, t 

 When the dodder has fastened upon a suitable host, sent 

 haustoria into it, and connected its own vascular tissues 

 with the corresponding ones of its host, it draws food 

 in abundance. Chlorophyll develops only in smallest quan- 

 tity in any part of it.| The dodder absorbs already elab- 

 orated all the sugars which it needs for the construction of 

 cell-wall, for the supply of energy liberated by respiration, 

 for the synthesis of amides, proteids, etc. Not having chlo- 

 rophyll, it lacks the means by which to securer the energy 

 needed for the elaboration of non-nitrogenous food, and for 

 this food it depends wholly upon its host. Presumably it 

 takes its nitrogenous food also in the soluble forms elabo- 

 rated by its host, though it modifies, assimilates, and in- 

 corporates this for itself. When the dodder, having fastened 

 upon an unsuitable host, is inadequately fed, it may become 

 green by the formation of chlorophyll in the chromatophores 

 always present in rudimentary condition in its cortical 

 cells. § It can thus add what it manufactures itself to the 

 insutBcient supply of non-nitrogenous food which it draws 

 from its own innutritions host. The dodder makes food for 

 itself only when it is unable to secure enough ready made. 



* See Chapter VI. for a discuBsion of the irritability of these and other 

 plants. 



f Peirce, G. J. L. c. 



t Ibid., A contribution to the physiology of the genus Cuscuta. Annals 

 of Botany, vol. Vm., p. 91, 1894. 



§ Ibid., L. c, p. 83. 



