BRYOPHYTA 207 



seen in the development of a foot and seta, as well as in the formation of 

 elaters. The foot absorbs food from the gametophyte. The seta places 

 the capsule in a favorable position with reference to spore dispersal. 

 Except in Riccia, the Sphaerocarpales, and a few other forms, a seta is 

 found in all bryophytes. Its absence in the Anthocerotales is correlated 

 with the indeterminate growth of the elongated capsule and in the Sphag- 

 nales and Andreaeales with the presence of a pseudopodium, the func- 

 tional equivalent of a seta. The development of a definite means of 

 dehiscence, seen in nearly all bryophytes except Riccia and the Sphaero- 

 carpales, represents an advanced feature. Elaters are present in almost 

 all liverworts but not in any of the mosses, where spore dispersal is aided 

 by other means, as by a peristome. 



Further progress of the sporophyte has come about through additional 

 sterilization and earlier diversion of potentially sporogenous tissue. Thus 

 an elaterophore is developed in some of the Jungermanniales. The for- 

 mation of a columella in the center of the capsule and of additional sterile 

 tissue in its outer portion is an advanced feature of the Anthocerotales 

 and Musci. The failure of a columella to develop in certain members of 

 each group indicates that the entire central region of the capsule was 

 originally sporogenous. The sporophyte reaches its highest development 

 in the Bryales, where the most extensive amount of sterilization seen in 

 all bryophytes has resulted in a greatly elongated seta and a capsule of 

 extreme complexity. 



The bryophytes show two well-marked lines of evolution with respect 

 to the sporophyte. The one, emphasizing spore dispersal, ends blindly 

 with the mosses. The other, in which the sporophyte attains par- 

 tial independence and exhibits indeterminate growth, culminates in 

 Anthoceros. 



Plan of the Mosses. In the mosses photosynthesis and fertilization 

 are functions of the gametophyte, the sporophyte being concerned mainly 

 with the production and dispersal of spores. An erect leafy gametophyte, 

 best developed in this group, favors photosynthesis but at the same time 

 hinders fertilization, since the sex organs are carried upward where it is 

 difficult for swimming sperms to function. The moss sporophyte is 

 highly specialized for spore dispersal, but without fertilization there can 

 be no sporophyte. It is evident, therefore, that combining photosyn- 

 thesis with fertilization as functions of the gametophyte is an unprogres- 

 sive tendency, because these two functions have different rerjuirements. 

 It follows that the mosses must be regarded as a blindly ending evolution- 

 ary line. 



Plan of Anthoceros. In the Anthocerotales the sex organs are borne 

 on a flat thallus, and so fertilization is easily accomplished. Although 

 still largely dependent upon the gametophj^te, the sporophyte develops 



