— 339 - 



covered stones and rocks at high-water mark with a dense matted growth. 

 My specimens were gathered in the middle of August and conserved in 

 alcohol; they are all sterile and attain a length of 1,5 mm. The head 

 is usually shorter than the stalk, but specimens having the head longer 

 than the stalk also occur, as seen by following measurements: 



The stalk 



The head 



Thickness 



Length 



Thickness 



Length 



above 



below 



above 



below 



44 p 



22 p. 



1233 p 



87 p 



49 p 



630 p 



37 - 



13 - 



1300 - 



77 - 



44 - 



460 - 



22 - 



12 - 



638 - 



28 - 



22 - 



900 - 



The head is usually distinctly clavate, sometimes nearly obovate and 

 occasionally nearly cylindric, especially in younger plants. Plants, in which 

 head and stalk insensibly merge 

 into each other (cfr. my fig. 2, b, 

 e, f, g and AI. Braun ]. c. Tab. I, 

 fig. 7 — 9) are frequent in my 

 material, but specimens having 

 the head distinctly separated from 

 the stalk with a constriction (fig. 2, 

 c, d, h) as figured by Börgesen 

 (1. c. fig. 106; cfr. also AI. Braun 

 1. c. Tab. I, fig. 14-15) also 

 occur. The distinctness of the 

 constriction is highly varying and 

 both of these forms are thus 

 connected with transitory forms. 

 The thickness of the membrane, 

 measured in the upper part of 

 the head, is usually about 7 t u, 

 but I have not rarely found it 

 varying from 3 — 10/./. The more 

 thinwalled specimens seemed to 

 be in a younger stage of age; the 

 more thickwalled plants usually 

 contained large quantities of starch. 

 The membrane is composed of 



Fig. 2. Codiolum gregarium Al. Br. 

 a a specimen with a branched head; b, e, 

 f\ g show specimens, in which head and 

 stalk insensibly merge into each other; 

 c, d, h showing the constriction h moreover 

 shows the transverse lavers of the stalk 



(compare the text). (40:1.) 

 three layers, as already noticed by AI. Braun (1. c): 1° a thin, external 

 layer (exoderma, cuticula AI. Braun) turning light yellow by chlor- zinc- 

 iodide, covers the whole surface both of head and stalk. 2° a thick middle 



