1916 Hurd; on Codium 111 



may branch just above the holdfast {Fig. 5) or at some distance from it 

 {Fig. 8). Thus the so-called holdfast-cushion is composed of the basal 

 ends of pith-filaments of the fronds with their interwoven branches, and 

 the erect utricles v.hich constitute the compact surface layer. These 

 utricles vary both in size and shape more than do those of the frond. 

 None were found bearing gametangia. 



Pith-filaments and utricles of the frond dift'er only in arrangement 

 from th'?se of the holdfast-cushion. The distance between two successive 

 utricles on the same filament may be anywhere from a distance so short 

 that the two utricles lie almost against each other, to as much as 6.5 mm. 

 (Figs. 18. 19). One filament was found which, though broken off 10.2 

 mm. from the end, had no utricles branching from it, nor did it have the 

 tip at all modified to form a utricle. 



In the formation of a utricle the end of a pith-filament expands and 

 the tip becomes very pointed. The points vary in length and acuteness 

 from long tapering ones characteristic of young utricles at the base of the 

 frond, to shorter more rounded ones at its tip. The point, or mucron, 

 is gradually filled nearly solid by the deposition of layer after layer of 

 material against the inside of the wall (Fig. 9). The utricle may still 

 be growing erect on the end of the pith-filament (Figs. 15, 16), or it may 

 already have bent at right angles, in which case it is growing horizontally 

 toward the surface of the frond (Fig. 17). From the base one or more 

 slender branches extend the pith-filament upward (Figs. 16, 17). Thus 

 layer after layer of utricles pile themselves on top of each other at the 

 tip of the frond and so increases its length. Young utricles are also 

 found anywhere along the frond growing from branches of these same 

 filaments. 



The utricles cease elongating when they reach the surface of the 

 frond. Mature utricles are .9-1.5 mm. long, and average 150-350 ^i in 

 diameter although one was measured that was 630 fx. They are club- 

 shaped, tapering at the base, broad and truncate at the end (Fig. 23). 

 There may be a slight constriction a short distance from the end or near 

 the base ; or there may be a considerable enlargement at or below the 

 middle. The outer end is densely green with chlorophyll, and in the older 

 utricles is often collapsed (Fig. 26). 



Utricles do not branch as Oltmanns (14) describes and pictures them 

 for C. tomentosum, but occasionally one is found with another utricle 

 growing from its outer end (Figs. 2. 6, 37). In one case, two smaller 

 utricles were seen originating one from either side of the mucron of the 

 main utricle (Fig. 33). Such irregular branching is more common in the 

 holdfast-cushion than in the frond ; and structures such as those shown in 



