154 SEAWEEDS 



there are borne the fertile whorls, each with a 

 secondary whorl and a terminal sporangium in the 

 middle. The ultimate whorl of these lateral 

 branches, overtopping the sporangia, form a kind of 

 cortex (as in the last genera), but without definite 

 facets externally. The space between them and the 

 axial cell is originally of slimy consistence, but 

 becomes the seat of incrustation. At the joints 

 there are no fertile whorls and the lateral branches 

 are here simple and decrease in length from 

 below upwards. It is a similar formation which 

 bears the terminal tuft of hairs. No observation of 

 germination has been made. 



A number of fossil genera, such as Decaisnella, 

 Haploporella, Dactylopom, Dactyloporella, Uteria, 

 and Polytrypa from the Eocene, and Munieria, 

 Gh/roporella and Triploporella of Cretaceous age are 

 certainly nearly related to the forms just described. 



The Reproductive Organs. Dasycladus is the only 

 genus in which the gametes have been observed. 

 We have seen that in Acetabularia the gametes 

 unite only with those from other gametangia, but in 

 Dasycladus the matter is carried a step farther, since 

 the gametes are here incapable of conjugation with 

 others from the same plant, and indeed they conju- 

 gate only with those of particular plants, not with any 

 other indiscriminately. It appears from this obser- 

 vation that though these gametes are apparently 

 all alike, there yet resides within them a definite 

 character indicating a difference of sex, though this 

 is not determinable by us from their structure. 



Judged by itself alone, Dasycladus appears to pre- 



