302 THE BRYOPHYTES 



THE ORIGIN AND EVOLUTION OF THE BRYOPHYTES 



297. The origin of the bryophytes. The origin of the bryo- 

 phytes is a mystery. They have of course arisen from the algse, 

 but there are no living algse that resemble the bryophytes at all 

 closely. Coleochcete 1 and the stoneworts (Charales) are the types 

 most frequently considered in relation to the mosses. But the 

 sexual organs of Coleochcete are one-celled, and the female organ 

 of Chara bears only a superficial resemblance to an archegonium, 

 while its antheridium is totally unlike any other male organ. 

 There must have been formerly some group of the algse, prob- 

 ably in the ChloropJiycece, distinguished by having many-celled 

 sexual organs from which the antheridium and archegonium of 

 the bryophytes arose ; for these complex sexual organs, together 

 with the characteristic sporophyte generation, constitute the chief 

 advance of the bryophytes over the algse. 



298. The evolution of the bryophytes. The evolution of 

 the bryophytes is clearly related to the change from the aquatic 

 habits of the algse to the land habit. Living upon the land exposes 

 the plant to the drying effects of the air and demands at once im- 

 portant structural adaptations, that is to say the plant must either 

 develop a firm cell structure so that drying up will not injure 

 the tissues seriously, or else it must maintain a constant con- 

 nection with water through the surfaces of filaments (rhizoids) 

 which are directly in contact with moisture. Many of the 

 mosses and leafy liverworts have solved the problem in the first 

 way and may become quite dry without serious injury. The Ric- 

 cia and Marchantia forms and Anthoceros, on the other hand, 

 are clearly adapted to the second alternative and die at once 

 if removed from water or moist earth. The creeping habit and 

 thallus structure of the simpler liverworts, while of advantage 



1 The fructification of Coleochcete has frequently been compared to a sim- 

 ple type of sporophyte, somewhat like those found in the Riccia group of the 

 liverworts. Recent investigations, however, indicate that this comparison 

 is not justified, and that the fructification is not sporophytic at all. See 

 Sec. 336 on the origin of the sporophyte. 



