164 BOTANY 
thelymitra (matkaika), a common native genus, self- 
pollination must often take place. Indeed, in the South 
Island the flower is almost always cleistogamic. It 
rarely opens, but almost invariably produces fruit. 
The cleistogamic condition doubtless serves to protect 
the pollen, which is reduced by rain to a useless pulpy 
mass. The flower limosella, a native plant of the 
snapdragon family, which grows in rain-pools, is 
eleistogamous if submerged, the perianth forming a 
water-tight envelope, under cover of which pollination 
takes place. Cleistogamy is evidently a protective 
adaptation that has helped some plants to survive in 
the struggle for existence, especially in a moisture- 
laden atmosphere. | 
Cross-pollination takes place where the stigma of 
a flower receives the pollen from another flower borne 
either on the same plant or on a plant of the same 
species. 
In diclinous plants, 7.e., those in which stamens and 
pistil are borne on different flowers, cross-pollination 
is a necessity. Diclinous (Gk. di two) plants are of 
two kinds, monoecious (Gk. monos single and otkos a 
house), where, as in the vegetable marrow and many 
pines, both pistillate and staminate flowers are borne 
on the same plant; and dicecious, where, as in the 
native clematis and pepper (kawakawa), they are on 
different. plants. The New Zealand flora is remarkable 
for its large number of dioecious plants belonging to 
a great variety of orders. For instance, the toa-toa, 
or celery-leaved pine, the mahoe, a tree belonging to 
the violet family, the coprosma, one of the coffee family, 
as well as the lawyer, pepper, and clematis are all 
dioecious, 
There is another device by which self-pollination is 
prevented and cross-pollination made a necessity. One 
essential organ may mature before the other. Where 
the anthers ripen and shed their pollen before the 
