Codium mucronatum 



Annie May Hurd, 

 University of Washington, Seattle. 



This paper is a morphological study of Codium mucronatum, the prin- 

 cipal object being to establish those characteristics which distinguish it 

 Irom other species, and those which form the basis for its varieties. 



Codium mucronatum grov. s fairly con:morly on the exposed rocky 

 shores of Puget Sound, in the lower littoral and upper sublittoral zones. 

 Muenscher (13) places it in the Ulva association. Plants are occasionally 

 found growing alone on isolated rocks, but usually they are very abundant 

 within a small radius. The gregarious habit and rather limited distribu- 

 tion would indicate either that the reproductive bodies are not carried 

 far, or that conditions favorable for their growth are very definite. The 

 plant body consists of a basal expanded portion, the so-called holdfast- 

 cushion, and one or more cylindrical dichotomously branched fronds grow- 

 ing from it. erect when small, drooping when older {Fig. 1). The whole 

 ]^lant is spongy in texture and dark green in color. The surface is more 

 or less rough, with a dull velvety appearance due to the protrusion of the 

 tips of the utricles. The fronds reach a maximum height of 40 cm. and 

 nr;^ from . !• to 1 cm. in diameter. The tips are blunt and rounded. The 

 branching is not always truly dichotomous for the frond may divide into 

 as many as five branches at one point. Several plants were found with 

 tlie fronds fairly covered from base to tips with young branches coming 

 out like large warts all over the surface. In some places these branches 

 had reached a length of 1 cm. and resembled young fronds starting out at 

 right angles to the old. 



The holdfast-cushion averages 3 mm. in thickness and has been 

 found covering an area of 100 sq. cm. In color and texture it is the 

 same as the frond. Growth takes place outward from the edge, leaving 

 the margin irregularly lobed. New fronds appear as small rounded 

 knobs on the surface of this holdfast-cushion. Xo matter how large the 

 elder })arts, new fronds continue to appear between the old fronds or 

 around the edge, singly or in groups. The largest plant observed, one 

 whose holdfast-cushion covered an area of 7. .5x13 cm., consisted of 20 

 large fronds and at least 50 young ones in various stages. 



From the knob-like stage the frond elongates and becomes a clavate 

 stalk slightly constricted just back from the ti]) (Fig. 1). The young 



(109) 



