6 j 6 Benson .—A00/ Parasitism in Exocarpus. 
can be no doubt that the haustoria do more than just tap the water-supply 
of foreign roots. Even animal organisms can be dissolved and absorbed. 1 
Exocarpus , indeed, more frequently than not wholly dissolves and absorbs 
the portion of the host root attacked. A vigorous attack on the host 
is likely to give the most abundant supply, and we find that all kinds 
of cells, except perhaps cork, yield to the attack. 
It is in the light of these observations that possibly we may find the 
significance of the granules in the phloeotracheides. Heinricher 2 refers to 
the structures as ‘ storage tracheides ’. But in such a case as Exocarpus , 
which under normal circumstances is exposed to drought conditions com¬ 
bined with much insolation, one cannot but look on these masses of cells 
interposed between the host and the mother root as serving as a filter. The 
granules by their precipitation leave the ascending sap less charged with 
dissolved carbohydrate, which is already present in excess in cortex and 
medullary rays. 
The different habit of Thesium , which is abundant on the moist Alps of 
Switzerland, may account for the insignificant development of granules 
in its phloeotracheides. 
Not only is the period of vegetative activity much shorter, but the host 
plants would be much richer in watery sap. 
Summary. 
On the roots of various plants of Exocarpus , chiefly Exocarpus cupressi- 
formis , Lab., growing in the Bush near Killara, N.S.W., were found 
innumerable haustoria which varied much in size and form. 
Their anatomy was examined and compared with that of Thesium 
haustoria gathered in August in Switzerland. 
The haustoria contained a large proportion of lignified tissue which was 
composed of elements for which the name ‘ phloeotracheides ’ is suggested. 
The tissue was not limited to two bands as is the case in the haustoria so far 
described of other Santalaceae. The function of these cells is discussed, 
and the probability advanced that they may be of service as a filter. 
I should like to take this opportunity of acknowledging my indebted¬ 
ness to Mr. Maiden, of the Botanical Gardens, Sydney, N.S.W., who was 
most helpful to me in various ways during my residence in that neighbour¬ 
hood. 
1 Cf. Barber’s Chrysalis, 1 . c., Santalum alburn , Part I, par. 9, and Figs. 15-17, PI. III. 
2 Heinricher, l.c., 1901, p. 725, footnote. 
