112 Pucjet kound Marine Sta. Pub. \'ol. 1, No. 12 



Figs. 2, 6, and 7. thoug-li ratlitr typical of the former, are rare in the 

 fronds. 



Old utricles are different from young ones not only in size and 

 shape but in the nature of the mucron. The youngest utricles have no 

 real mucron, but have a pointed tip shaped like a mucron with only a 

 thin wall around it {Ficj. 10). Utricles a little older can be found with 

 the very end solid, and the process of filling up the tip to form a mucron 

 indicated by the presence of layers of the substance not yet laid down 

 tightly against the preceding layers. This often results in what SvedeJius 

 (18) calls "das Gegliedtrtsein des INIucro," in v 'lich case there is a row of 

 compartments extending clear to the tip {iig. 9). Sometimes the mucron is 

 solid in which case it usually appears striated, faint lines indicating the 

 layers composing it. The older truncate utricles push up around the mucron 

 as the end expands and broadens so that the mucronate tip appears shorter 

 and less conspicuous. Contact with wave action, rock surfaces, and in- 

 vesting animals, all of which would contribute to the wearing off of the 

 originally long mucron, account in part for the fact that the mature 

 utricles have short, often rounded mucrons, and sometimes none at all 

 {Figs. 24, 40). This variation in the size and shape of utricle and mu- 

 cron is shown by a series of sketches in Fig. 24. 



Although one would suppose that the greatest number of young 

 utricles are found at the tip of the frond, on every plant examined the 

 greater number of slender, tapering long mucronated utricles were at 

 the very base of the frond, this type sometimes predominating for a dis- 

 tance of 6 cm. up from the base. The average size of utricles increased 

 as parts nearer the tip were examined, the largest ones being above the 

 center of the frond and continuing large up to within 2 cm. of the tip. 

 The average dropped very suddenly from there to the end, where the 

 utricles were of course all very small. To bring out these facts more 

 clearly measurements of utricles were made at various points along the 

 frond. A large number from each point were measured and the average 

 size computed. These averages for the same relative points on the dif- 

 ferent plants were in turn averaged to give the following results. The 

 average diameter at the base of the frond was 105 /x; 2 cm. from the base, 

 151 fji-, 4 cm., 168 //,; 6 cm., 189 fx; 12 cm., 220 /x; 14 cm., 312 fx; 16 cm.. 

 357 IX. This largest size predominates to within 2 cm. of the tip where a 

 perceptible decrease in the average begins. 



The slender utricles at the base of the frond were next examined to 

 determine if they were small because they were young, or because they 

 were physiologically different from those of the upper part of the frond 

 which bear the gametangia. In most cases it was very evident that they 

 were young, i.e., terminal. Therefore the time when these plants were 



