324 Peirce . — On the Structure of the Haustoria 
a constantly increasing distance from the host, an abundant 
and varied food supply, is as complete as in the Cuscutas. 
Treatment of thin sections of fairly developed buds of 
Balanophora elongata , with an aqueous solution of aniline- 
blue, shows that the fibro-vascular bundles contain sieve- 
tubes, and that both the sieve-tubes and the tracheids are 
united directly with the corresponding elements of the host. 
We see, then, that in parasites belonging to three distinct 
families (Convolvulaceae, Rafflesiaceae, Balanophoreae), sieve- 
tubes are developed in the haustoria. But no sieve-tubes 
were found in the haustoria of Viscum album. The parasites 
in the haustoria of which sieve-tubes have been found are 
absolutely dependent upon their hosts for food, they have no 
green tissues in which food can be elaborated. Viscum album, 
on the contrary, is abundantly supplied with chlorophyll, 
both in leaves and stem. It demands only that its host shall 
supply it with aqueous solutions of the crude materials from 
which it can elaborate its own food. It is a ‘ water-parasite ’ ; 
its host performs for it only the functions of a root, absorption, 
conduction, mechanical support. 
Is it possible that other green parasites are thus only 
partially dependent, and that they too, drawing from their 
hosts only unelaborated substances, form in their haustoria 
only tracheids or tracheae, and no sieve-tubes? I hope to 
pursue the question further. 
I wish to express my grateful appreciation of the en- 
couragement which Professors Strasburger and Schimper, and 
Dr. Schenck, by their kind criticism and suggestions, and 
the generous supply of material, have given me. 
Bonn am Rhein, February , 1893. 
