BIOLOGICAL SURVEY OK WOODS HOLE AND VICINITY. 



543 



Pyramid Rock 



Chart 273. — Distribution of algee on Spindle Rocks, September 19, 1904. 



This chart is introduced to show variations that may be present in the algal life on the same rocks 

 at the same season but in different years. It should be compared with chart 272, plotted September 2, 

 1905. The charts agree in having Ulva Lacluca var. rigida (5) as the conspicuous green alga on the tops 

 of the rocks. There was no Chordaria flagelliformis this season and consequently no zone of brown 

 alga;, although Scyiosiphon lomcntarius (26) grew in scattered patches. Nemalion multifidum (40) formed 

 a zone of thick growth above low-water mark (the dotted line) on rocks III, VII, VIII, and Pyramid 

 Rock. The most conspicuous zone was below low water and composed of Ccraniium rubrum (43) and 

 Polysiphoniafibrillosa (46). The Polysiphonia fihrillosa, which wasnot present at all in 1905, this season 

 took the place of Chordaria flagelUformis and Polysiphonia violacea (48), usually abundant, but scattered 

 plants of the latter were present. Chondrus crispus, as usual, was abundant, extending into deeper 

 water below the Polysiphonia. 



List of species: Ulva Lactucavai. rigida, 5, abundant; Scyiosiphon lomentarius, 26, patches on rocks; 

 Chorda filutn, 31, large beds; Laminaria Agardhii, 33, scattered patches; Fucus vesiculosus , 35, scattered 

 plants, Sargassum Filipendula, 36, few plants; Nemalion viullifidum , 40, abundant; Ccranmtm rubrum, 

 43, abundant; Polysiphonia fibrillosa, 46, very abundant, fringing rocks just below low- water; Polysi- 

 phonia violacea, 48, few; Chondrus crispus, 49, abundant. 



