136 NEW ZEALAND PLANTS. 
is abandoned by the birds, and the highly manured ground stands 
ready for plant-colonization. This is evidently fairly rapid. The 
first plant to settle on the abandoned land is the succulent-leaved 
Crassula moschata, usually a plant dwelling on saltish ground, which, 
stimulated by the enormous amount of available nitrogen, forms 
great patches 12 yards or so across. There may also be a cushion 
or two of Colobanthus muscoides—a plant elsewhere growing only 
on rocks drenched by sea-spray! As the manure becomes less 
powerful, the tussock-grass Poa foliosa gains a footing, and in course 
of time grassland is re-established. If the number of penguins in 
proportion to the size of the islands be taken into account, there can 
be no doubt that through their agency the plant-covering has been 
destroyed and restored again and again. ven the scrub-forest. of 
Olearia Lyallii and Senecio Stewartiae can have no chance of reinstate- 
ment, when once the trees die, so long as the penguins are present. 
These subantarctic islands offer another interesting example of 
a natural rotation of crops. Thus Disappointment Island, in the Lord 
Auckland Group, the scene of the terrible ‘‘ Dundonald” wreck, is 
the home of countless mollymawks (Diomedia melanophrys). Cast 
your eye over the dreary landscape and you will see brown grassland 
dotted with white birds, and here and there patches of vivid green. 
This last arises from the presence of the antarctic piripiri (Acaena 
Sanguisorbae var. minor). As the tussock, with its accompanying 
plants, is slowly but surely destroyed by the many generations of 
birds, the piripiri takes complete possession of the bare ground, thanks 
to its colonizing-power, for the barbed fruits adhere to the feathers of 
the young birds, and so are spread broadcast. The antarctic piripiri 
is really quite a rare plant in the tussock-grassland, and so there is 
here a remarkable example of a plant originally of little importance 
becoming, in a virgin vegetation, virtually a weed. But tussock 
will finally again predominate, and gradual alternate destruction and 
rejuvenation of the vegetation will always be in progress—a natural 
rotation of crops indeed, thanks to the presence of mollymawks. 
There yet remain for mention the Bounty Islands. So far as 
plant-life goes, their description is easy. Indiarubber-like masses of 
that great seaweed the bull-kelp (Durvillaea utilis), here yellow in hue, 
cover the rocks between the tide-marks, while, where the sea cannot 
reach, the glistening granite of these lonely isles is dimmed only 
here and there by the green stain of an alga, their sole land-plant 
