T3 
arrivals first in pools and later on the general surface of the 
littoral zone as first one and then another member of the 
summer population makes its re-appearance. 
Strictly speaking, in marine plant life, there is no hard 
and fast line to be drawn between “annuals’”’ and 
“perennials” ; distinct though these conditions may be 
when applied to land types. Indeed, neither term is 
applicable in its strictest sense to algal organisms. 
Analysis of the data collected over an extended period 
shews that many algae, of which Fucoids and Laminarians 
are outstanding examples, are always to be found on the 
sea-shore. These plants are to be regarded as the nearest 
approach to perennials that can be found among British 
marine algae. . 
Another class of algae comprising many genera is 
made up of plants that are to be found in profusion over 
extended areas during the greater part of the year, with a 
high point of abundance in the early summer. To such 
a category belong many filamentous Phaeophyceae (Ecto- 
carpus spp.) and many Rhodophyceae (Ceramium spp.). 
During the short intervening period representatives of these 
genera and species are still to be found, though in reduced 
stature and smaller number, in specially sheltered situa- 
tions. These plants are therefore present throughout the 
whole of the year but form a less conspicuous element of 
the flora in the winter and may even escape observation 
altogether. Many of these genera and species have been 
described in older algological treatises as ‘‘ summer 
annuals.” Clearly they are not truly annual nor yet are 
they perennial for no individual plant lives for the whole 
of one season ; indeed, its life-span is frequently limited 
to a few weeks, though the genus is maintained as a 
permanent component of the algal flora by successions of 
short-lived individuals. Such plants, whose numbers 
swell to a maximum in the summer but never quite reach 
