68 SEA A/OSSES. 



Cladophora arcta, Dillw. 

 The arched Cladophora, of which we give a fine 

 and characteristic illustration in Plate III., is named 

 from the peculiar habit of its growth. The branches 

 divide and subdivide by extremely acute angles, and 

 the ramifications are all very straight. This prevents 

 the unsymmetrical outline common to most plants of 

 this genus, keeps the branches somewhat close together 

 as they rise upward, and, at the same time, permits 

 them to separate gradually and symmetrically. This 

 gives the tuft its arched and graceful form, not unlike 

 the outline of our more perfect and beautiful elms. 

 This characteristic of form, the yellowish green color, 

 and the decidedly glossy or silky look, which the 

 plant usually presents when dry and pressed on paper, 

 makes its determination easy. Another peculiarity 

 which may be noticed in the dried specimen is the 

 disposition of the chlorophyl of the terminal branchlets 

 to collect in the extreme end cell, making that cell 

 have a distinctly darker green color than the cells just 

 below it in the branch. It is an annual. Mr. Collins 

 finds it common at Nahant and Nantasket, on rocks 

 between tides, from March to July. Miss Booth finds it 

 extremely rare at Peconic Bay, L. I. At Marblehead I 

 gathered it frequently during the summer months. It is 

 often found on the California coast, near Santa Cruz. 



