Root Parasitism in Exocarpus 
(with comparative Notes on the Haustoria of Thesium). 
BY 
MARGARET BENSON, D.Sc. 
With Plate LV and four Figures in the Text. 
D URING a visit to Tasmania in 1906 I was much struck by the 
contrast afforded by the Exocarpus shrubs (chiefly Exocarpus 
cupressiformis , Lab.)—the ‘ Native Cherry ’ of the Australian colonist—and 
the surrounding vegetation. The summer was exceptionally dry, and the 
vividly green switch-like habit of these plants made them very conspicuous 
against the uniformly grey background of the Eucalyptus £ Bush ’. In the 
autumn of the same year (April, 1906), on visiting New South Wales, I was 
able by the help of my kind host, Mr. William Benson, of Killara, to examine 
the roots for the parasitic connexions with other plants which I suspected 
might exist. 
We raised a number of young plants and washed the soil carefully 
away. By this means we were able to demonstrate innumerable con¬ 
nexions with small foreign roots. Some of these were mounted on the spot 
in glycerine jelly for examination under a low power of the microscope 
(Text-fig. 1). Other young plants were preserved in spirit and dispatched 
home for histological investigation. A small seedling was sent to me later 
by Mr. Benson, and has been photographed with some fruiting twigs of an 
adult tree. This shows the Thesium-Wke leaves of the young plant, which 
are progressively smaller on the lateral branches until they become almost 
entirely suppressed as in the case on the twigs bearing ‘ Native Cherry ’ 
fruits (PI. LV, Fig. A). 
On my return to England I found that Dr. Barber was engaged in 
describing the haustoria of several Indian genera of Santalaceae and of 
allied families. 1 
As Exocarpus does not occur in the Indian Flora, it was agreed that 
I should report on this genus. 
1 Barber : The Haustorium of Santalum album. Memoirs of the Dep. of Agriculture in India, 
vol. i, No. 1, Parts I and II, Jan. 1906 and July 1907. The Haustorium of Olax Scandens, ibid, 
vol. ii, No. 4, 1907. Parasitic Trees in Southern India. Proc. of the Cambridge Philosophical 
Society, vol. xiv, Part III. 
[Annals of Botany, Vol. XXIV. No. XCVI. October, 1910.] 
