THE BRYOPHYTA : MUSCI, THE MOSSES 



429 



them that separate Moss plants all grow so close together. As soon as the 

 leafy shoot has been formed it develops its own rhizoids and severs its con- 

 nection with the protonema which produced it. Since the protonema is 

 the product of a single spore it follows that all the plants produced on it 



BUD 



Fig. 415. — Mm'uin hormim. Origin of a leafy stem from a bud on a 

 branch of the protonema. The apical cell is diflferentiated at 

 the top of the bud. {After Muller-Berol.) 



will be of the same sex, and it is only by the intermingling of two protonemata 

 of different sex that male and female Moss plants can be produced side by 

 side. 



Alternation of Generations 



The life history of Mnium shows the same alternation of generations as 

 we found in Pellia. The Moss plant is a gametophyte, bearing either male 

 or female reproductive organs. As a result of a fusion of gametes a zygote 



.Oospore 



Sporogonium 



Spores 



Protenemo 

 Protenema 



Antherozoids 



Mnium Female 

 Plant 



Mnium Male 

 Plani 



Antheridium 



Fig. 416. — Life-cycle of Mnium hornum. 



