502 
May brook. — On the Haustoria of 
a zone of elongated parenchymatous cells. All roots were very carefully 
examined for the presence of sieve-tubes, but no trace of any was discovered. 
Fig. 2, B, shows two of these elongated parenchymatous cells pa., with their 
dense protoplasmic contents /., and large nuclei n., in longitudinal section. 
It is probable that transmission of organic food material takes place in 
Pedicularis root by osmosis, as Peirce 1 suggests for Arceuthobium occidentals, 
the complex materials passing from the elements of the host root through 
the thin walls of the parasitic parenchymatous elements by simple osmotic 
pressure. Now Benson 2 has suggested that the phloeotracheides of Exocarpus 
haustoria combine the functions of phloem and xylem. It seems probable 
that the tracheidal elements of Pedicularis root behave in much the same 
way, from the fact of their retention of protoplasmic contents. 
This absence of typical phloem elements is not characteristic of all root 
parasites. Barber 3 has demonstrated the presence of sieve-tubes in the 
roots, though not in the haustoria, of Olax scandens and Santalum album ; 
Peirce has shown that they exist in the roots and in the haustoria of 
Arceuthobium occidental ; and Benson has demonstrated their presence in 
the roots but not the haustoria of Exocarpus . Stephens , 4 however, failed to 
find any sieve-tubes in the roots of Striga lutea on which the haustoria were 
borne, and suggested that the transference of organic food might take place 
by osmosis. In the case of Pedicularis this seems to be most probable, 
especially in view of the nature of the xylem elements. 
The Haustorium. 
Du Sablon 5 has described briefly the anatomical development and 
structure of the haustorium, but for the sake of continuity and clearness 
a short account of the development will be given here. The haustorium 
arises in the hypodermal tissue of the cortex. The hypodermal cells of 
the cortex and the cells of the piliferous layer elongate enormously, and 
radial walls are formed in them. Tangential walls then follow rapidly 
in the elongated cortical cells, the cells of the piliferous layer, in 
contact with the host root, still continuing to divide by radial walls. 
Some of the outermost of these cells, that is, those farthest away from 
the surface of contact of the haustorium with the host root, elongate 
enormously, so that they have the effect of clasping the host root and 
acting as suctorial organs. Meanwhile division still continues in the 
cortical tissue, the endodermis even taking part in the division. Thus there 
1 Peirce, G. J. : Dissemination and Germination of Arceuthobium occidentals . Ann. Bot., 
vol. xix, 1905, p. 99. 
2 Benson, Margaret, 1 . c., p. 673. 
3 Barber, C. A. : Studies in Root Parasitism — The Haustoria of Santalum album. Mem. Dep. 
Ag. Ind., Bot. Ssr., vol. i, 1906-7. Studies in Root Parasitism — The Haustoria of Olax scandens. 
Mem. Dep. Ag. Ind., Bot. Ser., vol. ii, 1907. 
4 Stephens, E. L. : The Structure and Development of the Haustorium of Striga lutea. Ann. 
Bot., vol. xxvi, Pt. II, 1913. 
6 Leclerc du Sablon, 1 . c. 
