250 FIRST FORMS OF VEGETATION. 
similar adaptations, as their fronds are so in- 
crusted with lime as to render nutriment through 
the surface precarious. They resemble cacti, 
reticulated corals, flabelliform corallines, little 
wheels fixed on delicate stems, etc, and are very 
beautiful in their shapes or in their structure, 
when divested of the carbonaceous coating in which 
they are masked. Caulerpa, Halimeda, Acetabul- 
aria, etc., are examples of these curious organisms, 
which might easily be overlooked as corals. They 
are all natives of warm climates, such as New 
Zealand and Papua. The Caulerpa prolifera, like 
the Botrydium, consists of a single cell, though 
it is often a foot in length, and is branched with 
what has the appearance of leaves and roots. 
In pools and ditches of fresh water may often 
be seen vast masses of the two-pronged filaments 
of Vaucheria dichotoma, each filament being some- 
times two feet long, almost rivalling the huge 
masses of Cladophora mirabilis, and the Conferva 
melagonium of the Arctic regions. It differs little 
from the Botrydium except that the spherical 
vesicle of the latter is elongated into a simple 
or branched thread. Another species is very 
common on the ground in damp, dark situations, 
such as the ledges and crevices of cliffs in sub- 
alpine glens, and is also occasionally observed in 
gardens on walls or unfrequented walks, creeping 
