2 26 Alexander W. Evans, 



geb,** who notes also the fact that the two external rays are to be 

 compared with the "side lobes" in an ordinary dichotomy. In M. 

 polymorpha, where nine rays are commonly present, seven would 

 represent middle lobes and two, side lobes. Between the two side 

 lobes there is of course no group of archegonia, so that there are 

 eight groups for the entire receptacle, showing that three 

 dichotomies have taken place. 



The rays of the female receptacles vary in length, very much 

 as in the case of the male receptacles. There is, however, no 

 correspondence between the two. In M, polymorpha, for exam- 

 ple, the rays of the female receptacle are l6ng, and those of the 

 male receptacle are short, while in M. chenopoda the conditions 

 are reversed. The rays of the female receptacle differ also in 

 form, being flat in some species and cylindrical in others. When 

 they are flat they are often retuse or shortly bilobed at the apex, 

 and Goebel points out that a deepening of the apical sinuses 

 would lead to the condition found in M. geminata, where sinuses 

 instead of rays are present between the groups of archegonia. 

 In young receptacles the rays are strongly curved downward, 

 but they gradually straighten out if fertilization has taken place 

 and assume a horizontal position. 



On account of the strong intercalary growth which displaces 

 the archegonia to the lower surface of the disc, the portion of 

 the receptacle which is morphologically ventral is less extensive 

 than at first appears. The lower surface between the groups of 

 archegonia is ventral in character and the same thing is of course 

 true of the lower surface of the rays, especially when these repre- 

 sent the middle lobes of the branch-system. Even here, how- 

 ever, when the rays become cylindrical through intercalary dorsal 

 growth, the ventral surface is much less extensive than the 

 dorsal. In M. geminata the ventral surface of the rays is sit- 

 uated on both sides of the groups of archegonia. The ventral 

 surface is characterized by the presence of tuberculate rhizoids 

 and slender scales, the latter being sometimes branched and 

 strikingly different from the ventral scales of the vegetative 

 thallus. The dorsal portion (except where the archegonia are 

 situated) develops a complex system of air-chambers of the usual 

 type. 



** Unters. iiber Leberm. 6 : 34. 1881. 



