ME. E. M. HOLMES ON CODIOLTTM GBEGABIUM. 133 



has been found since that date in the United States by Dr. Farlow. 

 It is either rare or has often been overlooked. As seen in the 

 spot in which Mr. Cresswell pointed it out to me, it forms a 

 scattered velvety growth of a dark-green colour on the vertical 

 surface of the sandstone blocks of the sea-wall, where it is liable 

 to be wetted by the spray at high tide only, unless the sea be 

 rough, in which case the surf dashes over it. According to Mr. 

 Cresswell's observations, it grows also on the blocks of Devonian 

 limestone which form a portion of the same wall. He has found 

 it throughout the ivinter, year after year, in the same place, pre- 

 senting the same appearance to the naked eye, and the same cha- 

 racters under the microscope. In June he has found full-grown 

 specimens in a spot where the plant is within reach of every 

 tide. 



Braun has given a full account of the development and mode of 

 fructification of Codiolum gregarium in the 'Abhandlungen ' of the 

 Berlin Academy ; and to his valuable paper I am largely indebted 

 for the details here given. 



The full-grown plant consists of a simple stalked cell of a cylin- 

 drical form, clavate at the upper end, and containing obovate zoo- 

 gonidia. The whole plant is only 1-1| inillim. long, the club, or 

 upper portion containing the zoogonidia, being usually \ millim. 

 long and JL-— ^ millim. thick, and the hyaline stalk 1± to 3 times 

 as long as^ the club, and ^-^ millim. thick, gradually tapering 

 towards the rounded base. 



The youngest specimens present the form of an obovate cell, 

 the first stage in the growth of which is the appearance of a 

 hyaline elongation of the narrow end, which gradually increases 

 until the plant becomes of the adult stature, the clavate portion 

 increasing in diameter very slightly until the stalk has attained 

 its full development, i. e. two or three times the length of the club. 

 Under the action of chemical reagents the cell-wall (cytioderm) 

 is seen to be composed of three layers. The outer, or exoderm, 

 covers the whole plant, and is a thin uniform membrane. The 

 inner, or endoderm, is similar in character, but is found only as 

 the sac which contains the zoogonidia, the whole of the interior 

 of the stalk being filled with the middle layer, which consists of a 

 firm gelatine ; but between the inner and outer layers of the club 

 it forms a thin stratum only. In the young state the cavity of 

 the club is filled with green endochrome (cytioplasm), in which 



