Chapter IV.—A REPORT ON THE ALG! OF SPINDLE ROCKS, WOODS HOLE 
HARBOR. 
That many alge have well-defined seasons of vegetative growth is well known, but 
there have been very few detailed or intensive studies of particular regions covering 
sufficiently long periods to give important conclusions. It is certain, however, that 
there are seasonal floras which follow one another over the same area in much the same 
manner as terrestrial floras. This study was undertaken in the hope that observations 
on a particular group of rocks at Woods Hole at various seasons might bring out some 
important facts on the life habits of the alge of this region. 
The rocks selected for the study seemed particularly well adapted for the purpose. 
They were a group of bowlders called by the writer Spindle Rocks because, lying off 
Grassy Ledge at the entrance to the ship channel in the passage of Woods Hole, they 
bore a light on an iron spindle. Unfortunately for the continuation of the work, the 
rocks were removed during the summer of 1906 by dredging operations of the Govern- 
ment to widen the ship channel, and the spindle was shifted to another position. 
The destruction of the old group of rocks of course ended the observations, which 
had been in progress for 15 months, beginning in the summer of 1904 and extending 
through the summer of 1905. ‘The studies over this period, however, are of considerable 
interest, since they cover the seasonal changes of one entire year. They are illustrated 
by 8 charts, which are selected from a series of 10 made during this period. 
Spindle Rocks, as shown on the charts (267-274), was a group of 10 bowlders, the 
smallest having a length of about 5 feet and the largest of about 9% feet. Some portion 
of each rock was exposed at low water and all of the rocks were covered at high tide. The 
rocks lay to the north or right of the entrance to the ship channel leading through the 
passage from Woods Hole Harbor to Buzzards Bay and were an outlying portion of 
Grassy Ledge. The rocks were exposed to very swift tide currents, which flow through 
the channel at a rate of 5 to 8 miles an hour. ‘The ledge fell off abruptly on all sides, 
but between the rocks the depth was 1 to 6 feet. The outlines of the bowlders were 
plotted in a chart showing their form and position as viewed from above. The low-water 
mark was sketched for each rock by a dotted line, and above it two other lines indi- 
cating tide marks 2 and 5 inches, respectively, above low water. A plate was made from 
the original drawing and charts were printed to be used for making the records. In the 
work of preparing this chart the writer received much assistance from Mr. F. W. Cushwa. 
The study was concerned entirely with the flora over the tops of the rocks and 
below low-water mark to a depth of 3 to 6 feet. Each species was given a number, and 
charts were plotted at intervals, the numbers with accompanying notes showing the 
position and abundance of the alge over the rocks. It was found most convenient in 
practice for two persons to take the record of the ledge, one making the examination and 
the other recording by number on the printed chart the position of each species. At 
the end of the study the list of species was arranged in the order adopted in the Catalogue, 
476 
