Cc. A. BARBER. on 
but remaining white and clear. A much more pronounced 
duramen is to be seen in the haustoria of Buckleya described by 
Kusano attached to various Coniferous roots, the duramen of the 
haustorium keeping pace in growth with that of the host, as does 
the cambium. In Olax the protoxylem at an early stage becomes 
discoloured in like manner and a few cases have been noted in 
which the inner layers of the secondary wood are also thus 
discoloured. This discolouration is partly due to brown substance 
filling the lumina of the parenchyma between the vessels (Plate 
IX, fig. 1 and diagrams 6—10). 
16. An old stage of Olax haustorium is shown in fig. 1 of 
Plate X, the host being Casuarina equisetifolia. The sucker 
lobes, working along the cambial line, have almost completely 
surrounded the vascular cylinder of the attacked root. Neverthe- 
less its abundant development of new secondary bundles, both 
in the centre and in the cortical wings, suggests that the 
Casuarina root has as a whole suffered comparatively little 
injury. The haustorium, on the other hand, as is usual in such 
old stages, has cells emptied of all contents, the layer of cells in 
contact with the vascular cylinder is pronounced and the remain- 
ing tissue remarkably clear. This clearness of tissues has been 
regarded as a sign of waning activity of the whole organ in 
Santalum and it has been assumed that such haustoria are 
moribund, a point of view adopted by Solms-Laubach’ in his 
study of Thesiwm. The section now being studied is of further 
interest in that it shows the connection between haustorium and 
mother root and the development of the upper part of the 
collapsed layers. 
The collapsed layers have in this case reached their utmost 
development and extend upwards for a short distance on either 
side of the vascular loop. The lower and middle portions have 
already been described in detail in paragraph 13; the upper 
portion is, like them, developed entirely from cells of the cortex. 
1 H. Graf zu Solms-Laubach, Ueber den Bau u.Entwickelung der Ernahrungsorgane 
Parasitischer Phanerogamen. Jahrb, f, wiss. Bot. Vl. 1867-68. 
3 
