﻿A MEXICAN AYTONIA 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 211 

 Anna M. Starr 

 (with plates i-iv and four figures) 

 To this genus Engler and Prantl refer six names, among 

 which Aytonia Forst and Plagiochasma L. are most familiar in 

 botanical literature. Leitgeb (14) made a study of Plagiochasma 

 cordatum, P. intermedium, P. crenulatum (Gottsche), P. appendi- 

 culatum, and P. Aytonia. He gives an account of the appearance, 

 the position, and the formation of the antheridial and archegonial 

 receptacles, describing the order of the appearance of the arche- 

 gonia and the origin of the archegonial cavity and of the involucre. 

 He describes also the protective scales about the receptacles and 

 their origin from a single row of cells, and accounts for the stalk 

 of the receptacle as simply a dorsal outgrowth of the thallus. He 

 concludes with an account of the structure of the sporogonium and 

 its dehiscence. 



The material for this investigation was collected in Mexico in 

 1908 by Dr. W. J. G. Land and the late Dr. Charles R. Barnes. 

 Most of it came from the rocky sides of the deep canyon of the Rio 

 Santiago in the state of Jalisco near Guadalajara, the rest from 

 Carrizal in the state of Vera Cruz. The species cannot be deter- 

 mined definitely. Of the four Mexican forms described by Gott- 

 sche, it resembles most closely his Plagiochasma crenulatum, but 

 differs in that the ventral scales reach the margin of the thallus. 

 This Mexican form presents some variations in external appearance, 

 and an examination of structure offers some details not covered 

 by Leitgeb, so that it has seemed worth while to give a descrip- 

 tion of the external appearance, an account of the internal struc- 

 ture of the thallus and of the formation of rhizoids, a complete 

 description of the development of the air cavities of the archegonial 

 receptacle, and an addition to the history of development following 

 fertilization. 



Botanical Gazette, vol. 61J 



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