1906] BRIEFER ARTICLES 145 
2. Lije relation.—The shore just below low tide to a depth of 6™ is 
taken up by shorter, broad algae, mostly brown, many green, a few red; 
limited up shore by the grinding wave-washed rocks as the tide level 
varies, and by the baking heat of a summer sun during low spring-tides; 
limited downwards by the decreasing sunlight; we find on this strip the 
battle ground of the green and brown algae, species against species. Nereo- 
cystis, with its tough, flexible, cattle-whip-like stalk 12 to 21™ long, rises 
from the bottom in the deeper waters, a veritable Esau, surrendering to 
the Jacobs the coveted strip and wresting from the undesired, compara- 
tively unoccupied territory beyond, a highly successful existence. The 
stalk is firmly anchored to the rocks below by holdfasts covering an area 
as Much as 30°™ in diameter. So strong and tough is the stalk, and so 
firm the attachment, that often a pull of several hundred pounds is neces- 
sary to loosen the plant; and then the stalk more often than the holdfast 
gives way; but a large plant, avoiding quiet waters, needs a firm hold, 
and one occasionally finds the plants washed ashore with holdfasts dragging 
rocks as much as 20°™ in diameter, The admonition to “build upon a 
rock” holds for N: ereocystis, and the rock must be a big one; those which 
“build upon sand” are washed away before they reach the adult stage. 
This is one of the reasons why it grows upon reefs. 
Algae love moving water, but few can afford it. Moving water facili- 
tates gas exchange by carrying away that ladened with evolved and lacking 
In desired gases, and by not depositing suspended materials like quiet 
water. A layer of beach washings over a plant absorbs sunlight, one of 
the scarcer commodities of marine algae, any diminution of which only 
those most favorably located can afford. Nereocystis, by its firm anchorage 
and long stalks, surmounted by a bunch of tough blades 3 to 9™ long but 
harrow for their length, rides easily in flowing water, and chooses for its 
home the rocky, clean-swept, tide-washed promontories, where the current 
keeps its blades horizontal. 
elow 6™ the brown algae rapidly decrease, and dredging in Puget 
Sound shows that below 12™ they are exceptional. They need light. It 
is well known too, that the decrease in light downward in water is rapid. 
This makes the surface the most desirable location. But shore forms, at 
the surface at high tide, are stranded high and dry at low tide; and those 
at the surface at low tide are covered at high tide, the depth depending 
“pon the difference between high and low tide. This constant change in 
Water level is one of the greatest difficulties with which, seaweeds have to 
‘ontend. We see at once that marine algae have a very serious problem, 
to steer clear of the Scylla of darkness on the one hand, and, on the other, 
