8 STUDIES IN ROOT-PARASITISM. 
Zizyphus SJujyuba and Opuntia Dillenr. It is not, however, 
possible to form any definite conclusions on this point without a 
very great deal of study in other localities. All that can be said 
is that, from the very limited series of plants in which the roots 
have been laid bare, there are some grounds for assuming a certain 
amount of preference for certain hosts. 
6. Inthe many haustoria examined in the preparation of 
this paper, a number of young ones, attached but not yet pene- 
trated, were encountered, and a study of these has proved to be 
of exceptional interest (Plates III—VI). No attempt will be 
made here to trace the embryonic stages of the haustorial devel- 
opment or to determine the tissues of the mother root from 
which they were derived. It will suffice to say that there are 
evidences that the development of the haustorium from the 
mother root is similar to that described by Leclere du Sablon’ for 
Thesivm and assumed by me for Santalum, but it will serve a 
better purpose to deal with this subject in several species together 
and the necessary material has not as yet been collected. 
In its first appearance the haustorium of Olax scandens 
resembles that of Santalum album closely. The root-system of 
the pot-plants which were expected to furnish many young stages 
proved disappointing, but a certain amount of material was col- 
lected in nature (Plate IT, fig. 2). It may be noted that even 
in the youngest stages the haustoria were smooth, although the 
roots on which they occurred were well clothed with root-hairs. 
This appears to be rather unusual among root-parasites. Root- 
hairs have frequently been noticed on the haustoria of Santalum, 
while they appear to be a constant feature in the Rhinanthacee. 
The haustoria in Olax appear to be able, as in sandal, 
to develop without the aid of foreign root-stimulus, but 
proofs of this are not so clear as in that plant. Be that as it 
may, many of the haustoria become fairly large before they 
! Leclere du Sablon, Recherches sur les Organes d’Absorption des Plantes Parasites 
(Rhinanthacer et Santalacer). Ann. dad Se, Nat., Bot., Ser. VII, vol. vi, pp. 90-117, 1887. 
