673 
Benson.—Root Parasitism in Exocarpus. 
has been described by Leclerc du Sablon 1 for the apices of such cells 
in Rhinanthaceous haustoria, are often non-striated and thin-walled. I have 
noted what I believe is a nucleus in one apex, and there can be no doubt as 
to their apical growth. 
Fig. 3, PI. LV, shows the apical part of one of these cells abutting on 
the starch-containing cells of a medullary ray of the host root. 
If we take all these facts into consideration and remember that no true 
phloem occurs in the haustoria of any so far described root parasite, we 
realize that these cells have a complex nature. 
They collect and act as the pathway for the hydrolysed products 
of solution of the host cells and deposit in their lumina granules differing 
from those occurring elsewhere in the root. They are lined with protoplasm, 
but contain no nucleus, and in these respects resemble sieve-tubes. 
They are, however, lignified, and it has been possible in many cases to 
demonstrate that their end walls are absorbed as in open tracheides. 
It will be convenient, therefore, to refer to these cells as phloeotracheides, 
for they afford an example of the combination of the structure and function 
of phloem and xylem elements. 
The Granules in the Phloeotracheides. 
The only previous record of these granules, as far as I know, is due to 
Heinricher, 2 who made a careful investigation of the chemical and physical 
properties of apparently comparable bodies in the conducting cells of the 
haustoria of Lathraea. He came to the conclusion that they were probably 
of the nature of amylodextrine. 
In the footnote of a later paper 3 he again refers to these granules, and 
states that Wegler believes them to be present in the haustoria of all the 
Rhinanthaceae. Heinricher uses the expression, ‘die Tracheidenreihen 
haufig mit Amylodextrinstarke erfiillt sind.’ He found also the amylodex¬ 
trine bodies in smaller amount in the cells of the parenchyma of the tracheide 
head. In Exocarpns when granules occur elsewhere than in the phloeo¬ 
tracheides they are starch granules, and are not stained by the aniline. 
The grains, however, are much smaller than those of the cortical cells. 
The amylodextrine bodies abut so closely on the wall that I am 
inclined to regard them as occasionally deposited upon the inner surface. 
One of the most remarkable things about them is their early appearance in 
cells only just cut off from the meristem. They seem to appear simul¬ 
taneously with the lignification of the wall. Their size bears a rough 
relation to the width of the bands of thickening in any given cell. Thus 
1 Leclerc du Sablon: Organes d’absorption des plantes parasites. Annales des Sci. Nat., 
7th series, vol. vi, PI. II. 
2 Heinricher, Cohn’s Beitrage, Band 7, 1895, p. 344; also PI. IX, Fig. 7. 
3 Heinricher, Die griinen Halbschmarotzer. Pringsheim’s Jahrbuch, 1901, iii, p. 725. 
