MODIFICATIONS OF ORGANS. 109 
insects. Similarly, the very perfect pitchers of Nepenthes— 
a genus which occurs chiefly in the Malaysian region—have 
been shown by Sir J. Hooker to exert a very powerful diges- 
tive action upon nitrogenous matters. 
Parasitism, or the peculiar habit which certain plants 
have acquired of growing upon other plants and abstracting 
their nourishment from them, is possessed by several species 
of plants in varying degrees of perfection. Thus, some are 
called root-parasites, because they establish themselves when 
young on the roots of their host, and are thus saved the neces- 
sity of producing roots of their own. 
The only parasite* of this class known to occur in New 
Zealand is a most remarkable and rare species—Dactylanthus 
taylori—which appears to have been found only in two locali- 
ties in the North Island, and which grows on the roots of 
Fagus (Native Birch) and Pittosporwm (Mapau). 
An English root-parasite, Bartsia viscosa, has been intro- 
duced into parts of the colony, but it does not show any para- 
sitic tendency under its altered surroundings. 
A remarkable kind of parasitism has been acquired by the 
Dodders (Cuscuta), and by Cassytha, a genus allied to the 
laurels. One species of Cuscuta is indigenous to this country, 
and two or three have been introduced from Europe ; Cassytha 
ig also represented by a local species. The plants of the 
genus Cuscuta are allied to convolvuluses, and, like them, 
each begins its existence as a herb with a twining stem. As 
soon as the young stem comes into contact with the stem of a 
plant suitable for a host, it twines round it, and at the sur- 
faces which are in contact it develops small sucking discs. 
When a sufficient number of these have been produced the 
root in the goil dies away, and in future the parasite lives 
upon its host. Cuscuta is quite destitute of leaves, and con- 
sists only of thin thread-like stems, on which clusters of 
flowers and fruit are produced. Its leafless character is pro- 
bably due to the fact that its suckers can only extract from 
the plant on which it grows those portions of the sap which 
have already been assimilated. 
The most complete kind of parasitism is that found in 
Mistletoes, of which several species of Loranthus, Tupera, 
and Viscum occur in New Zealand. These plants have lost 
the power of growing in soil. The seed is dropped by a bird 
on the branch of a tree, and germinates there, the radicle 
penetrating the bark. The plant thus established becomes 
quite amalgamated with its host. But it differs from Cuscuta 
pers Burope plants of the genus Huphrasia (or Eyebright) are usually 
parasitic on roots; apparently this peculiarity has not been observed in 
any of the New Zealand species of the genus. 
