72 THE RELATION OF PLANTS TO TIDE-LEVELS 
water. It grows most abundantly where partially shaded, but it is apparently 
killed out by the denser shade of large masses of Fucus and Ascophyllum or 
even by tufts of Bostrychia. 
RHODOPHYCEZ. 
The only red algee found on the wharves are Bostrychia rivularis, Delesseria 
leprieuru, Hildenbrandia prototypus, and Porphyra laciniata. Their distribu- 
tion is indicated on plate 1x. 
Bostrychia: The dense, wiry, blackish tufts of this alga reach a length of 
2 or 3 cm. and stand so close together as to cover the surface for an area of 
several hundred square centimeters. It occurs on both wood and stone on all 
the wharves, of both sides of the harbor, in spots devoid of the rockweeds, 
though often more or less overhung by them. Its vertical range extends from 
about 2.5 to 6.5 feet. In shaded cracks of wet piles or dock logs Bostrychia has 
been found abundantly as high as 7 feet, and a few plants were found at 7.3 
feet. This level is higher than that at which any other red alga occurs in Cold 
Spring Harbor or the neighboring parts of Long Island Sound. Aside from 
Hildenbrandia no other red alga occurs on the wharves or beach above the 4-foot 
level, which is the upper limit of Porphyra. 
All the fruiting plants of Bostrychia found in summer bore tetraspores. In 
April 1911 and November 1912 the plants were of the same size and had as 
actively growing initials as in midsummer. The species is evidently perennial 
and seems not to be injured by freezing, even at its extremely exposed positions 
far above the mean low water level. It is evident from the tide-curves (plate 
xxiv) that Bostrychia at the 7.3-foot level must go without being wet by salt 
water for several days in succession during each series of neap tides. It might 
chance to be splashed by an occasional wave. Aside from the fact that at this 
height it must often be washed with rain there is no suggestion from the distri- 
_ bution of Bostrychia that it can endure immersion in fresh water. It has not 
been found close to fresh-water outlets, either in walls or on the natural 
shores. 
Delesseria: This alga, though occasionally found in summer, on logs on the 
bottom, has not been seen on the wharves, except in September 1911, when it 
was unusually luxuriant. It flourished also at this time at a few points on the 
shore. It was found abundantly on piles and stones of the north end of the 
wharf of the Research Laboratory, between the 2 and 3 foot levels. The patches 
were here often several square centimeters in area and the plants 20 to 30 mm. 
high. Those that were fruiting showed only tetraspores. It is, of course, 
possible that this alga is more abundant in winter than in summer, though 
the brief examinations made in April and September did not show it to be at all 
common. 
Hildenbrandia: This ubiquitous incrusting alga forms hundreds of red 
patches, often several centimeters in diameter, on the otherwise bare stones 
of the wharves. Such patches of Hildenbrandia we have already described 
(p. 31) on pebbles in the rivulets along shore. The lower limit of Hildenbrandia 
is at about mean low water and its upper limit, on the wharves and in the 
fresh-water rivulets, is at 6 or 6.5 feet, rarely at 7 feet. The vertical distribu- 
tion of this alga is therefore as wide as that of the most widely distributed 
Schizophycere and Chlorophyceer, like Spirulina or Enteromorpha clathrata. 
