136 



MOSSES AND FERNS 



CHAP. 



and the outer cells begin to grow out into root-like processes 

 which push down among the cells of the thallus and obviously 

 serve the purposes of haustoria. Leitgeb states that the foot 

 arises only from the lowest of the primary tiers of cells, but in 

 most of my sections of the earlier stages the fact that the foot 

 was composed of two distinct layers of cells, corresponding in 

 position to the two lower tiers of cells in the embryo, was very 

 obvious (Fig. 70, E). 



FIG. 70. Anthoceros Pearsoni. Development of the embryo X'3oo; A, C, E, median 

 longitudinal sections; B and D, successive cross-sections of embryos of about the 

 age of A and C respectively. In E the archesporium is differentiated. 



The origin of the archesporium in Anthoceros was in the 

 main correctly shown by Leitgeb, but I find that the extent of 

 the archesporium is less than he represents. In PI. I. Figs. 3 

 and 10 of his monograph on the Anthoceroteae, he figures the 

 archesporium as extending completely to the base of the 

 columella. A large number of sections w r ere examined, and 

 in no case was this found to be so. Instead, it was only from 

 the cells surrounding the upper half of the columella that the 

 archesporium was formed. Previous to the differentiation of 



