212 Alexander W. Evans, 



The complex epidermal pores of Marchantia are of much 

 interest. They are of the dolioform or barrel-shaped type, that 

 is, the opening of the pore is surrounded by two series of cells 

 arranged in concentric rows, one series projecting more or less 

 above the surface of the thallus, the other projecting into an 

 air-chamber. Although pores of this type are found on the 

 sexual branches of most of the Marchantiaceae, the only genera 

 where they occur on the vegetative branches are Marchantia, 

 Preissia, and Biicegia. Even in Marchantia, as shown by Kamer- 

 ling,^^ immature shoots sometimes produce pores of the simple 

 type found in most of the other members of the group. 



The first attempt to utilize the structural features of the pores 

 for taxonomic purposes seems to have been made by Voigt.^^ He 

 studied eight species of the genus, and showed that the number 

 of pores in a given area, the number of rows of cells surround- 

 ing a pore, and the number of cells in a row were fairly constant 

 for each species. Stephani also has drawn specific characters 

 from the pores, but certain of his distinctions, as will be 

 shown below, are subject to variation and must be used with 

 caution. 



In the case of M. polymorpha the pores have been repeatedly 

 figured, although the published illustrations are not all of the 

 same degree of excellence. Among recent figures those by Voigt, 

 Kny, and Miiller^^ bring out most of the essential points. Accord- 

 ing to Voigt, whose account of the pores is imusually full, the 

 opening is surrounded by five circular rows of cells, three belong- 

 ing to the upper and two to the lower series, but both Kny and 

 Miiller state that the upper series is normally composed of only 

 two rows making four rows in all, a statement which agrees 

 with the writer's observations (see Fig. 2, A, B). Under some 

 conditions the number of rows may be reduced to three or even 

 to two. In the upper series each row is composed (in most 

 cases at least) of four cells (Fig. 2, A, B), and immediately 

 surrounding the pore a circular membranous ridge is present, 

 probably representing, as in the simple pores of Targionia,^^ a 

 collapsed series of cells. This ridge is shown by Voigt (/. i), 



"Flora 84 (Erganzungsb.) : 57. 1897. 



" Bot. Zeit. 37 : 74i. 1879. 



" Rabenhorst's Kryptoganien-Flora 6 : /. J<?7. Leipzig, 1907. 



" See Deutsch, Bot. Gaz. 53 : 494. /. 9. 1912. 



