214 BOTANY 
rapidly than the moss. These polypody mats often 
contain a considerable amount of soil so that now 
there is a chance for the creeping miihlenbeckia, 
which, with its masses of slender wire-like shoots, 
forms a hummock that is the most efficient collector 
of wind-drift the lava-stream possesses. 
Now may appear terrestrial astelias, the koromiko 
and the myrsine, to be followed by the pohutukawa, the 
broad-leaf, the akeake, and, in many places, the manuka. 
The establishment of a flora under such conditions is 
truly one of the triumphs of Nature. How many 
millions of seeds must have been blown from the main- 
land, have fallen on the island and germinated before 
a single seedling was able to establish itself? We ean 
imagine the fortunate combination of cireumstances 
that contributed to the result—an early autumn, a 
moist, mild winter, followed by a cool, wet summer, 
Then, perhaps, one among many thousand seedlings 
would get its roots favourably placed to secure the 
highest possible amount of the scanty moisture the 
dust in some erevice and the porous lava beneath were 
able to supply. 
SuMMARY. 
A Struggle for Existence goes on among plants, in 
which those best adapted to the particular environment 
survive, and those not so well adapted go to the wall. 
Some plants are suited to a great variety of environ- 
ments; others only to special environments. The latter 
form plant societies. Water supply is the chief factor 
in determining the plants that shall constitute any 
society. 
Hydrophytes. Water plants have thin epidermis, 
reduction of roots, wood-vessels and supporting 
tissues. The submerged leaves are much divided, 
the floating ones rounded and entire with stomata 
on upper surface. They grow rapidly and reproduce 
