671 
Benson.—Root Parasitism in Exocarpus . 
the lignified bands on the walls of the cells in which they lie are stained 
pink with the safranin, the constituent parts of the haustorium are effectively 
exhibited in the series of sections from which the diagram is constructed. 
The Phloeotracheides. 
These cells, the so-called ‘ vessels ’ of previous writers on Santalaceous 
haustoria, are sufficiently unique to merit description. 
They appear to be common to all root haustoria, although arranged in 
several different ways. 
In radially symmetrical Exocarpus haustoria they form a flask-shaped 
sheath to the central hyaline core, the neck of the flask abutting upon the 
host, and being surrounded by nucleated club-shaped cells which probably 
have a secretory function. 
Text-figs. 3 a and 3 b. Enlarged drawings of parts of an Exocarpus root with haustorium. 
Text-fig. 3 a. Surface, S, and transverse, 
T, sections of the phloeotracheides of a hau¬ 
storium containing granules of various sizes. 
N = a nucleated thin-walled cell accompanying 
the phloeotracheides. x 230. 
Text-fig. 3 b. A longitudinal section of 
part of the xylem of an Exocarpus root show¬ 
ing two tracheides, Tr, with bordered pits, P. 
Two medullary ray cells ( M ) filled with starch 
grains abut on the tracheides, and one has 
thrust in a thylosis, Th , which also contains 
starch, x 230. 
The phloeotracheides, in all but three cases that have come under my 
observation, contain granules of a carbohydrate. 
Although in some cases these phloeotracheides, when stained with 
safranin and aniline, bear a superficial resemblance to the sieve-tubes of 
some Ferns, there is no ground for thinking the pellicles are callose in 
nature nor that they are continuous through the thin areolae. The explana¬ 
tion of their presence is, probably, that the residual protoplasm of the 
partially differentiated tracheide receives such an abundant supply of hydro¬ 
lysed cellulose that part of it is deposited as amylodextrine. 
