32 THE RELATION OF PLANTS TO TIDE-LEVELS 
Agardhtella is a coarse and rather cartilaginous species which is found 
abundantly in parts of the Outer Harbor and which often drifts into the Inner 
Harbor. It has not been found within our limits fixed to anything larger than 
small pebbles which are dragged about by the stiff, bushy plants. In some 
seasons dozens of these, and still larger numbers of entirely free plants, are 
tumbled about over the bottom, below the 1.5-foot level. 
Ceramium rubrum is abundant on Zostera in the Inner Harbor and is also 
found occasionally on pebbles or shells in the Inlet at 2,300 north by 1,000 to 
1,200 east at mean low water and below. Its relative, C. strictum, has not been 
found, except on Zostera. 
Chondria also has been recorded but once since our work began (in July 
1908), though it was often seen in earlier years in the same place,—2,200 to 
2,300 north, on the east side of the Inlet, at about the —1-foot level. In the 
one case recorded carefully the plants were about 1 dm. high, and all of them 
were tetrasporic. During the early years of this study Chondria was abundant 
in the Outer Harbor just outside the Inlet. At these times floating plants of 
Chondria were common in the Inner Harbor. The fixed plants outside the 
Inlet have disappeared almost completely during the last few years, and with 
them, of course, the free plants in the Inner Harbor. No cause has been 
discovered to which this disappearance of the Chondria, and of other red 
alge also, can be attributed with certainty. It seems probable that it is 
related to the sudden covering of large areas of the bottom by mussels which 
occurred in 1907. 
Perhaps the greater rarity of certain alge of the Inner Harbor in recent 
years is due to the greater distance over which the spores must come from 
areas outside it, where the plants are abundant and constantly present. It 
seems evident that fewer of the spores can reach the Inner Harbor from an 
_ area 2 or 3 miles away than from one 200 or 300 yards away, though as a matter 
of fact we have no certain evidence of the endurance of these spores or of their 
ability to remain afloat for so long a time. 
Delesseria is a smoky green, inconspicuous alga that has been found only 
once within the limits of the belt that we are discussing—at 1,750 north by 1,070 
east at the 1-foot level. It is more frequent at slightly higher levels, as we 
shall see later. 
Gracuaria is found in small numbers attached to pebbles and shells at levels 
between —2 and +1.5 feet on the bottom of the Inlet. It is sometimes also 
found being washed about over the bottom of the harbor, either entirely free or 
else dragging about with it the small pebble or shell on which it has grown. Both 
attached and free plants of Gracilaria have become less frequent of late years, 
probably for reasons identical with those suggested in speaking of Chondria. 
Grinnella is a broad, sheet-like alga which is quite frequent in the Outer 
Harbor. When our work began attached plants of it were abundant every 
summer in the shallow branch of the Outer Harbor directly north of the Inlet. © 
In 1906 three or four attached plants were found near 175 north by 625 east. 
These in all probability had been carried in by the tide and had dragged their 
small supports with them. Our records for 1907 show that half a dozen attached 
plants of this species were found in the Inlet between 2,200 and 2,400 north 
near mean low water. Plants which are entirely free are still found drifting 
over the bottom of the harbor, but while in earlier years these could be seen by 
