PHYLOGENY OF AXGIOSPERMS 289 



1. Spore-production was the first office of the sporophyte, and the 

 spore-phase has constantly recurred throughout the descent of the 

 Archegoniatae ; the spore-bearing tissues are to be regarded as primary, 

 the vegetative tissues as secondary, in point of evolutionary history. 



2. Other things being equal, increase in number of carpospores is 

 an advantage; a climax of numerical spore-production was attained 

 in the homosporous Vascular Cryptogams. 



3. Sterilization of potential sporogenous tissues has been a wide- 

 spread phenomenon, appearing as a natural consequence of increased 

 spore-production. 



4. Isolated sterile cells or layers of cells (tapetum) served in many 

 cases the direct function of nourishing the developing spores, being 

 themselves absorbed during the process. 



5. By formation of a central sterile mass (columella, etc.) the spore- 

 production was, in more complex forms, relegated to a more superficial 

 position. 



6. In vascular plants, parts of the sterile tissue formed septa, par- 

 titioning off the remaining sporogenous tissue into separate loculi. 



7. Septation to form synangia, and subsequent separation of the 

 sporangia, are phenomena illustrated in the upward development of 

 vascular plants. 



8. Such septation may have taken place repeatedly in the same 

 line of descent. 



9. The strobilus as a whole is the correlative of a body of the 

 nature of a sporogonial head, and the apex of the one corresponds to 

 the apex of the other. 



10. Progression from the simpler to the more complex type de- 

 pended upon (a) septation, and (6) eruption to form superficial appen- 

 dicular organs (sporangiophores, sporophylls) upon which the sporan- 

 gia are supported. 



11. By continued apical growth of the strobilus, the number of 

 sporophylls may be indefinitely increased. 



12. The sporophylls are susceptible of great increase in size and 

 complexity of form ; in point of evolutionary history, small and simple 

 sporophylls preceded large and complex ones. 



13. In certain cases foliage-leaves were produced by sterilization 

 of sporophylls. 



This theory means that the leafy sporophyte is derived from 

 such a sporophytic structure as is displayed by the sporogonium 

 of Bryophytes; but, as suggested by Klebs and Lang, it may 

 have had an entirely independent origin, and may have no 

 phylogenetic connection with such a structure as a sporogonium. 

 This view, together with its possible relations to the question 

 of antithetic versus homologous origin of the sporophyte, has 



