1916 Hind; on Codium dimorphum 213 



the widest part of a utricle is often about 300/x from the tip {Figs. 3-5). 

 They taper gradually back to the size of the pith-filament and are not cut 

 off by plugs ; therefore unless the utricle is a lateral branch, its lower end 

 is indefinite and its length cannot be measured. 



Unlike the utricles of C. mucronatum, those of C. dimorphum branch 

 in a very characteristic manner {Figs. 2, 3). A young branch starts as 

 a protrusion of the utricle and grows upward. Before long a plug forms 

 in the base and the young utricle bulges downward below the place of 

 attachment. This bulge elongates at a more rapid rate than the utricle 

 above, and forms a long "dangling" pith-filament several millimeters in 

 length. These new jDith-filaments and utricles remain attached to the 

 old one, and when the former reaches the surface of the rock on which 

 the plant is growing it probably forms a holdfast {Fig. 6). In preparing 

 slides for microscopic examination the attachment is often broken so that 

 filaments are found with the lower end rounded and not expanded into a 

 holdfast, and which can be traced to the terminal utricle without finding 

 any apparent connection with the rest of the plant {Fig. 5). There does 

 not seem to be any constant number of branches. One utricle was found 

 with six branches and at least eleven scars where other filaments had 

 been broken off. 



The young utricles taper at the end and have hard thickened tips. 

 As they grow older the diameter increases and the end becomes truncate. 

 After reaching a certain size, 75-140|ii, the tip ceases to increase in diam- 

 eter and enlarges 225-300/x back from the end. The oldest utricles are 

 very large, sometimes without clorophyll, and often collapsed at the end. 



The end walls of the utricles may be thin, or characteristically thick- 

 ened. They may be as much as 300/i, thick, and when thick are distinctly 

 striated, as if formed in layers. This "dimorphism" is one of the points 

 upon which Svedelius (12) bases this species. However, some plants are 

 found without any thick end walls, and others have only the thick walled 

 type; but quite often tlie utricles of the upper surface are thin walled, 

 while those on the under side of the lobes and around the margin of tlie 

 thallus are thick walled. Altliough observations arc rather limited, it 

 seems to be the case that the plants of the more exposed localities have the 

 thicker walls. 



It is not unusual in this species to find one utricle growing from the 

 tip of another. In fact, this may occur three or four times in succession, 

 so that a structure like that shown in Fig. 8 is quite often seen. The 

 utricles occasionally divide dichotomously at the tip {Fig. 12). They are 

 also sometimes found with a slender jnth-filament growing from the end,, 

 which might later develojj a terminal utricle {Fig. 11). 



