NUTRITION 87 



taining in their leaves and in the cortex of the young and 

 even older branches, an abundance of chlorophyll in nor- 

 mally effective chloroplastids. They are plants which can 

 and do photosynthetically manufacture from water and 

 carbon-dioxide all the non-nitrogenous food which they 

 need. Elevated far above ground on the branches of oaks, 

 poplars, apples, etc., they must draw from their hosts the 

 water which they combine with the carbon-dioxide absorbed 

 by their own leaves. Since the water in plants is a dilute 

 solution of a large variety of matters, chiefly mineral, the 

 mistletoe absorbs from its host these needed substances 

 also. Their absorption is accomplished through peculiarly 

 modified roots called haustoria, the wood or xylem elements 

 of which connect directly with the wood elements of the 

 vascular bundles of the host. Through the xylem the water 

 absorbed from the soil and the mineral salts dissolved in 

 it are transferred to the leaves. The mistletoe, tapping the 

 water-conducting tissues of the host, establishes a water- 

 conducting system continuous with that of the host, and so 

 secures a supply of water and mineral salts as constant and 

 as abundant as that of the host. On the other hand, the 

 chief paths of transfer for elaborated foods, nitrogenous as 

 well as non-nitrogenous, are furnished in higher plants by 

 the phloem elements of the vascular bundles, but from these 

 the foods are distributed osmotically through parenchyma 

 cells to the tissues needing them. The phloem elements of 

 the haustoria of Viscum and Phoraclendron are not con- 

 tinuous with those of the host. * From this fact it has been 

 inferred that mistletoe does not absorb elaborated foods of 

 any sort from its host, that it is, therefore, only a "water 

 parasite.' 7 This inference is scarcely defensible, though in the 

 absence of direct evidence to the contrary the supposition 

 is justified that Viscum robs its host of much less elaborated 

 food than those parasites which have a direct phloem, as 

 well as xylem, connection with their hosts. 



* Peirce. G. J. On the structure of the haustoria of some phanerogamic 

 parasites. Annals of Botany, vol. VII., pp. 317, 318, 1893. Cannon, W. A. 

 The anatomy of Phoradendron villosum. Nutt. Bull. Torrey Bot. Club, 

 vol. 28, 1901. 



