CHLOROPHYCE® 165 
are produced in Siphonocladus as a result of injury of 
the thallus. 
The Geographical Distribution.—The distribution 
of the order is mainly tropical—only the genera placed 
here with hesitation — Halicystis and Blastophysa 
reaching the North Atlantic and North Sea. 
Valonia, with about fifteen species, is of wide occur- 
rence in the warmer seas; Apjohnia, with two species, 
is found in Australia and at the Cape; Siphonocladus, 
with several species, in the Mediterranean and in 
tropical seas ; Chameedorts (one species) in all tropical 
seas ; Dictyospheria (two species) in the West Indies 
and Australia; S¢vwvea (six species) in the tropics for 
the most part; Boodlea (one species) in the Pacific ; 
while Microdictyon and Anadyomene, with six or seven 
species each, are also mainly tropical. 
CLADOPHORACES. 
General Characters —The thallus is always a row 
of single cells in some cases branched, in others 
simple, and since these cells contain each several 
nuclei, it is very difficult to say where the dividing 
line is to- be drawn between Cladophoracee and 
Valoniacee—between the old order Stphonew and 
the other Chlorophycee. In the typical Cladophor- 
acce the filaments, whether branched or simple, grow 
erect in tufts, but in Gomontia the habit of the whole 
plant is modified by its living within the substance of 
shells which the filaments perforate. Reproduction is 
effected by the conjugation of equal gametes, and by 
