Algal Genera Acicularia and Acetabulum 327 



As has already been described for Acetabulum Androsace and 

 A. crenulatum, the young shoot in Acicularia Schenckii is an erect 

 cylindrical or often somewhat curved tube, with a tapering sub- 

 acute or rounded apex. In two cases out of the many young 

 plants examined, we have observed the beginnings of a dichoto- 

 mous branching (Fig. 22) ; in all other cases the shoots have been 

 simple. The development of the primary whorls of articulated 

 sterile branches offers no peculiarities worthy of special mention 

 except the fact that we have been unable to find more than one 

 whorl of such branches persisting at any one time. Harvey* 

 figures in the young plant of Acetabulum crenulatum previous to 

 the formation of the fertile disc three whorls of sterile branches and 

 the beginning of a fourth and Woronin f gives a similar figure for 

 Acetabulum Androsace. In Acicularia Schenckii two or three 

 whorls are sometimes developed in succession before the formation 

 of the disc, but in such the lower whorl has fallen by the time the 

 next higher appears, and only scars remain to testify to its former 

 existence. We have found no conclusive evidence that a plant of 

 A. Schenckii ever matures more than one fertile disc. One case 

 has been met with, in which a single shoot bore the beginnings of 

 two discs separated by the scars of a whorl of sterile filaments, 

 but in this the lower of the two rudiments showed unmistakable 

 indications of arrested development in small size, unequal growth, 

 and occasionally exfoliated members, and the suspicion that it was 

 destined to no further growth seems well grounded. A case in 

 which the development of a disc seems similarly arrested and the 

 continuation of the axis shows the beginnings of a sterile whorl 

 is represented in Fig. 20. Fig. 21 shows the scars of a delapsed 

 disc and the prolification of the axis, but there is no proof that 

 the delapsed disc reached maturely or that, if it did, another 

 disc would actually reach the spore-bearing stage. Yet it must 

 be admitted that cases like those just described suggest the pos- 

 sibility that a plant may occasionally mature two discs. 



With the aid of material preserved in formalin, we have been 

 able to follow out stages in the development of the disc which 

 have been observed hitherto only in Acetabulum Androsace and 



*Ner. Bor.-Am. 3 : pL 42. 1858. 



f Ann. Sci. Nat. Bot. IV. 16 : //. 8. 1862. 





