Chapter IV.— A REPORT ON THE ALGM OF SPINDLE ROCKS, WOODS HOLE 



HARBOR. 



That many algae 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 fife habits of the algae 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 algae 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, 

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