BRYOPHYTA Byal 
an absorbing organ, the foot, which attaches the sporophyte 
to the gametophyte (Fig. 410). 
Alternation of generations. ‘I'he gametophyte that bears eggs 
and sperms is followed by a sporophyte that produces spores, 
and this in turn by a gametophyte. There is, therefore, an 
alternation between a gametophyte, that bears eggs and sperms, 
and a sporophyte, that produces spores. This alternation of 





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Fic. 402. Section of thallus of Riccia, showing mature sporophyte 
The sporophyte, or sporangium, at this stage consists of a mass of spores, the sterile 
covering having disappeared. The spores lie free in the venter of the archego- 
nium, the inner layer of cells of which has practically disappeared. (x 80) 
gametophytes and sporophytes is known as the alternation of 
generations or the alternation of gametophytic and sporophytic 
generations (Fig. 438). 
As a result of the fusion of the nuclei of the egg and sper- 
matozoid the fertilized egg has twice as many chromosomes as 
either the egg or the spermatozoid. In other words, the egg 
or the spermatozoid has an 2 number of chromosomes, while 
the fertilized egg has a 2 z number. The 22, or double, number 
persists in the sporophyte until spore mother cells are formed. 
Each spore mother cell, by two successive divisions, gives rise 
