420 JOURNAL OF SCIENCE, 
sap which they draw into their own stems is chiefly in the unas- 
similated state. Therefore the parasite has to assimilate this crude 
sap by means of its own leaves. A chapter could be written on the 
peculiarities of the mistletoes alone, without exhausting the subject. 
Thus it is very common to find them parasitic on one another; 
Tupeia often occurs on Loranthus, and the reverse is as common. 
Again, in Australia, two species, each the type of a distinct genus, are 
almost exactly like Loranthus, but are terrestrial. - Now an interesting 
question might be worked out. Are Nuytsia floribunda and Atkin- 
sonia ligustrina slightly altered descendants of the original forms. 
from which the whole order arose, or are they species in which 
the parasitic habit has been lost? In favour of the first hypo- 
thesis it might be argued that the order is largely represented 
in Australia, and that its nearest allies are Proteacee and 
Santalacee, two orders well represented there, in fact, the first 
is a typical Australian order. In favour of the second hypothesis. 
is the fact that each genus is only represented by a single 
species, whereas if the genera were very old we should expect 
to find intermediate forms; and further, it is much the simpler expla- 
nation, for it is evidently an easier modification for a parasitic plant 
to revert to the terrestrial habit, than for a terrestrial plant to become 
a parasite. I have here a singular form of retrograde development in 
a mistletoe. The genus Viscum to which the English mistletoe 
belongs, is represented in this country by two species, V. salicornioides 
and V. lindsayi. Both are lcafless plants, having flattened or rounded 
branches, whose surfaces perform the leaf-functions. Now in 
Australia there are three Viscwms, one is leafy, one has angular or 
rounded branches like our V. salicornioides, and one has flattened 
branches like our V. lindsayi. Evidently we have here some clue to 
the origin of these species. 
A parasite of a different kind is the dodder. Dodders belong to 
the genus Cuscuta, and are parasitic convolvuluses. Like the major 
convolvulus of our gardens, the seed, on germination, sends up a small 
slender stem, which at once commences the rotating movement com- 
mon to twiners. In the course of its movement it comes into contact 
with some stem of clover or other plant, and at once begins to twine 
on it. As soon as it has made several revolutions, small sucking discs 
are formed along the surface of contact, the root in the soil dies away, 
and the young dodder depends on its host for all its nutriment. It 
has no leaves of its own, because as its food supply is all drawn from 
the outer layers of the plant on which it grows, it has been already 
assimilated for it. But when it has reached a sufficiently mature age, 
it puts forth on its thin naked branches numbers of small pink 
flowers. These plants are great pests to the agriculturist, for they _ 
sometimes destroy whole fields of clovers and other plants. We have 
one species of Cuscuta indigenous to New Zealand, but I have no 
specimens of it. Similarly, in a very different order of plants from 
the Convolvulacee, viz., the Laurines, to which the true Laurel 
belongs, a genus of parasites termed Cassytha has arisen. These have 
exactly the same characters in their parasitism as Cuscuta. The 
seeds germinate in the soil, and the young stem begins to revolve. 
As soon as it has caught a stem to twine on, the sucking discs are 
developed, the terrestrial root dies, and the plant lives exclusively on 
