STERILISATION 



Such examples serve to show that there are good grounds for holding 

 that sterilisation of individual cells of the sporophyte, which by their origin 

 are to be recognised as potentially fertile, does take place ; and that such 

 cells may be diverted to a temporary, or to a more permanent use 

 in connection with the production of spores. Thus we are justified 

 in holding that sterilisation, which is the initial factor in the 

 working hypothesis sketched in the previous chapter, has been actually 

 operative. 



It will be impossible here to enumerate all the cases where evidence of 

 sterilisation of potentially fertile cells has been brought forward ; but some 



of the more prominent instances of it 

 will be quoted. At present it is the 

 mere fact of sterilisation which is before 

 us, not the biological consequences 

 which follow in facilitating the nutrition 

 or the dispersal of spores, nor yet the 

 morphological advances which may 

 result. These aspects of the matter 

 will be left over till the several groups 

 of the Archegoniatae are specially 

 discussed. 



Among the Liverworts the simple 

 Ricciaceae have centrally an undiffer- 

 entiated sporogenous tissue; but as a 

 rule in the Marchantiaceae and Junger- 

 manniaceae the almost spherical mass 

 of sporogenous tissue becomes differ- 

 entiated as development proceeds : 

 cells, singly or in groups, instead of 

 undergoing the tetrad-division, are 

 developed in a vegetative manner, 

 either as nutritive cells (Sp/iaeroawf>its) r 

 or as elaters of various form and 

 arrangement (compare Fig. 46, of 

 Aneitra). In the Anthocerotaceae, on the other hand, the archesporium 

 is a dome-shaped layer surrounding a central columella ; but the products 

 of this layer do not only form spore-mother-cells, but also numerous 

 sterile cells arise from it, which develop as an irregular network enclosing 

 the mature spores. In point of fact, in the Liverworts it is the exception 

 rather than the rule for the whole of the sporogenous tissue to be fertile, 

 though this is the case in the simplest of them. 



In the Musci, on the other hand, the whole of the cells developed 

 from the definite, single-layered archesporium normally produce spores ; 

 but the archesporium is relatively small compared with the bulk of the 

 young sporogonium : it shows an apparently arbitrary limitation at its 



FIG. 48. 



Median longitudinal section of a sporogonium 

 of Sfihafnuiii, with bell-shaped archesporium. 

 X 170. (After Waldner.) 



