CHAPTER XVII. 



THE ESTABLISHMENT OF A FREE-LIVING SPOROPHYTE. 



So far the shoot only of the sporophyte has been the subject of discussion : 

 it remains to consider the question how the sporophyte, originally dependent 

 upon the parent prothallus, became established as a free-living organism 

 on the soil. There will be no two opinions which of the principal 

 regions of the independent sporophyte, the shoot or the root, was of 

 prior existence : it is a necessary outcome of the evolution of the neutral 

 generation as sketched above that the shoot was first established, as a 

 body dependent on the gametophyte ; it carried out primarily the function 

 of spore-production, but ultimately also, as we have seen, that of vegeta- 

 tive nutrition. The root is essentially an accessory, which made its 

 appearance after those earlier steps were past; it arose from its 

 primitive state of dependence to an existence free from the parent 

 gametophyte. 



Comparison of living plants indicates, however, a probability that the 

 initiation of a root-system followed closely upon the adoption of a free- 

 living habit : for roots are present in free-living Pteridophytes with very 

 few exceptions, and are, as a rule, formed early in the embryology. It 

 seems doubtful, even in the few exceptional cases, whether the rootless 

 condition is not due to reduction, rather than representative of a primi- 

 tive rootless, but free-living sporophyte. Among the Pteridophytes roots 

 are absent in the Psilotaceae, also in certain Hymenophyllaceae, and in 

 Salvinia : it seems probable that reduction will correctly account for it in 

 such specialised forms as the Hymenophyllaceae ; and also in Salvinia, 

 with its peculiar floating habit : the question in the Psilotaceae is more 

 problematical, and their rootless condition may perhaps have been really 

 primitive, though in the absence of any knowledge of their embryos there 

 is no clear indication that it was so : moreover, their habit is so peculiar 

 as to make any conclusion difficult. Rootless Phanerogams also exist, 

 but there is no reason to regard them as other than results of relatively 

 recent reduction. Accordingly, it may be concluded that there is little 





