77 
Cutler ia multifida (Grevl). 
developing summer sexual plant, Aglaozonia a slow-growing 
perennating winter form ; and that these two growth-forms 
had become complementary in structure and habit, as well 
as in reproductive functions. 
A consideration of the conditions under which these two 
plants live in the Bay of Naples shows, however, that this 
does not represent the whole truth. The majority of the 
most interesting of the summer annuals growing in shallow 
water on the southern shores of England are, in the Bay of 
Naples, early spring- and even winter-plants ; while others, 
on the other hand, retire to deeper water. A few examples 
will make this clear : thus, Cutleria at Plymouth grows in 
company with abundant Spor'ochnus, A rthrocladia^ Stilophora , 
Asperococcus bullosus , Dictyota , and such Florideae as Du- 
dresnaya coccinea and Scinaia furcellata ; all these forms 
reproducing freely in July and the beginning of August, 
and growing in 2-3 fathoms of water at a temperature of 
i8°C. From data given by Falkenberg for the Bay of 
Naples, it appears that Sporochnus and Arthrocladia flourish 
also there in July and August, but at a depth of 20 
fathoms ; Stilophora follows the Cystoseira zone at a slightly 
less depth and grows in early summer ; Asperococcus bullosus 
also in spring and summer, varying from 1-8 fathoms ; 
Dudresnaya at 2 fathoms in March and May ; and Scinaia 
at the same depth from February to June, although the latter 
has been dredged at Messina in July at 1 5 fathoms. 
Of the plants with which Cutleria grows in English waters, 
therefore, some retain at Naples the same annual period, 
but live in far deeper water ; but more generally the depth 
of water remains fairly constant, while the season of the 
year is changed. There can be little doubt that the two 
determining factors of external environment are temperature 
and intensity of sunlight, with the latter being associated 
a greater degree of purity in the water, which in the Bay 
of Naples allows vegetation to flourish as far out as 40 
fathoms, while, in the immediate vicinity of Plymouth Sound, 
only scanty traces are met with at even 10 fathoms. Cutleria 
