1915] HUTCHINSON— PELLIA EPIPHYLLA 141 



archegonal form (G, If I) the first wall (1) is not median, but some- 

 what laterally placed and inclined; there is no wall no. 3; the 

 section corresponding to the quadrants C and D does not divide, 

 but remains as a sterile wall cell. Wall 2 again cuts off a section 

 corresponding to quadrant A, which also persists as a sterile wall 

 cell. A periclinal wall (5) divides the section corresponding to 

 quadrant B into a wall cell and a spermatogenous cell. Three 

 of the quadrants have become sterile. Starting with the Mar- 

 chantiales form of antheridia, by the sterilization of alternate 

 quadrants the Jungermanniales form is derived; and by the 

 sterilization of three quadrants the archegonial form results. The 

 sterilization sequence corresponds to the time sequence as de- 

 scribed above. 



Only one step is lacking in this series to complete the transition 

 from the antheridium of Marchantiales to the archegonium, namely 

 the reduction of the spermatogenous mass into a single row of cells, 

 only one of which, the egg, shall be functional. Such transition 

 forms have been described by Davis 6 in Marchantiales. The 

 writer has seen such "archegonia" with gamete masses in sections 

 prepared by Dr. W. J. G. Land. The antheridial forms of P. epi- 

 phylla furnish evidence that the various types of antheridia and the 

 archegonium have had a common origin, possibly gametangia resem- 

 bling in structure the antheridium of Marchantiales. 



Relationships 



The genetic relationships of P. epiphylla, because of its diversity, 

 present a rather complex problem. With respect to its relation 

 to other species of the genus Pell in, if the other species retain 

 throughout life the form of apical cell ascribed to them, it would 

 follow that P. epiphylla has branched sooner from the general 

 line of progress and has retained and developed generalized char- 

 acters. As a member of the Jungermanniales, this species is 

 acrogynous in the sense that growth is checked, apical growth is 

 stopped, by the production of archegonia. It differs from the more 

 characteristic Acrogynae in having several regions of growth, each 

 of which is checked in the same way. It is possible that acrogyny 



6 Davis, B.M., The origin of the archegonium. Ann. Botany 17: 477-492. 1903. 



