The Causes of the Zoning of Brown Seaweeds, i 99 
were covered by the sea was the primary factor in determining the 
zoning. The rock-pool vegetation confirms this. The seaweeds 
growing high on the shore were never, or very rarely, found in 
pools, whereas those which were only uncovered at the lowest 
tides were found in a great majority of rock-pools. 
ZONING SEAWEEDS 
L 
YOUNG SEAWEEDS CROWN Wt. h HO ' AUGUST/ »0OS 
IN WA TEH ti MRS . 0*iV ! lib. 
FOCUS V ESiCULQSUS 
if tM 
FUCUS CEr>an:i&i£ 
Fig. 28. In water 11 hours; dry 1 hour. x |. Fucus serratus grew 
rapidly at first, but flagged later. Fucus vesiculosus grew rapidly; no specimen 
died. Ascophyllum nodosum grew well; no specimen died. Fucus ceranoides grew 
slowly ; no specimen died. 
There are three phases of the plant’s life history which may be 
influenced by drying, viz :— 
1. Germination of the zygote. 
2. Vegetative growth. 
3. Reproduction and dispersal of gametes or zygotes. 
The first and last of these phases offer some difficulties to experi- 
