THE BRYOPHYTA: HEPATICAE, THE LIVERWORTS 



395 



make their way in the water film, which under damp conditions covers the 

 thallus, and enter the neck of the archegonium, where they penetrate to the 

 oosphere before losing their flagella. Fertilization is effected by the union 

 of the nucleus of one antherozoid with that of the oosphere. 



In all organisms which are fertilized by free-swimming gametes, some 

 attractive force must operate to guide them towards the females. In the 

 Bryophyta this is known to be the chemical attraction of sucrose, cane sugar, 

 which diffuses from the mucilage at the open neck of the archegonium. 

 This is an important example of chemotropism, which we shall discuss 

 further in Vol. III. 



The Sporogonium 



After fertilization the oospore divides by a transverse wall into two cells, 

 the lower of which plays no further part in development, whilst the upper 

 cell continues to divide, first by a vertical wall and then by one at right angles 

 to it. By further tangential cell divisions a layer of cells is formed which 

 becomes the outer covering of the young embryo. Its further development 

 consists in the formation of a capsule or theca at the top, and a stalk or 

 seta below (Fig. 377). The capsule is formed from the upper part of the 



ELATER 

 ARCHESPORIUM 



CAPSULE 

 WALL 



SUSPENSOR 



Fig. 377.— Pe///a epiphxUa. Development of sporogonium. A, First division of oospore. 

 B, Further division of upper cell. C and D, Further stages in development. E, Diflfer- 

 entiation of archesporium and capsule wall. F, Sporogonium at resting stage. {After 

 Hofmeister.) 



