38 
The Queensland Naturalist June, 1939 
its metabolism; it is now known that “spike” is a virus 
disease. 
The mistletoe family consists almost entirely of stem 
parasites, but in Australia we have two terrestrials — 
Nuytsia (the West Australian Christmas Tree) and 
Atkinsonia. Nuytsia , already mentioned as a tree with a 
trunk longer than that of any erect tree, parasitises 
almost any root that it encounters. Not uncommonly it 
will send its roots into a vegetable patch and attack a 
whole row of carrots. Atkinsonia is a New South Wales 
species which has not yet been investigated, but would re- 
pay examination. 
The root habits of the genus Olax of the family 
Olacacae have not been exhaustively examined in Queens- 
land. Olax imbricata, of the Philippine Islands, has 
haustoria as large as those of the sandalwood, and one of 
our Queensland species, 0. retusa , though having smaller 
haustoria, is definitely parasitic. Just to what extent 
root parasitism is developed in this family remains to be 
shown ; it may be worth while to examine Ximenia ameri- 
cana, the yellow plum, and even members of the related 
family, Icacinaceae, to which belong the common rain 
forest trees Villaresia Moorei (Ohurnwood) and Pennantia 
Cunninghamii (Brown Beech). 
Under the Bentham & Hooker system of classifica- 
tion, a remarkable American genus, Krameria , was in- 
cluded in the Leguminosae. Krameria canescens is a sort 
of parasite which has been examined in detail by Cannon. 
Its placing in the Leguminosae is by no means unanimous. 
(It is placed in Polygalaceae in the Engler & Prantl 
system and by Hutchinson). 
This root parasitic habit is something otherwise un- 
known in Leguminosae, which have specialised in another 
direction, a mutual istic symbiosis with nitrogen fixing 
bacteria. These bacteria attacking the roots from the soil 
give rise to galls on the roots; to that extent they must be 
regarded as disease-producing organisms. The root host, 
however, has become part of the normal make-up of 
leguminous plants. The bacteria fix atmospheric nitrogen 
and on their death the plant receives the benefit of it. 
Nitrogen is one of the most important elements in plants, 
but it must be taken in from the soil in combined form. 
The vast reservoir of gaseous nitrogen in the atmosphere 
is of no direct use to the ordinary green plant. Experi- 
ments carried out under sterile conditions have so far 
