



93.] Morphology of Spore-producing Members. 173 



The first pages are devoted to the discussion of points of general 

 morphology of the sporophyte, as it is seen in archegoniate plants, 

 together with a sketch of the history of opinion as to the morpho- 

 logical " dignity " of the sporangia and their relation to the parts 

 (usually sporophylls) which bear them. The position of Goebel is 

 adopted, that sporangia are as much organs, sui generis, as are shoots, 

 roots, &c., no matter where they may be seated. It is customary to 

 assume that the ontogeny will serve as a guide to the history of 

 descent in plants as in animals. As applied in detail to the sporophyte 

 generation this assumption cannot be upheld : for the conclusions 

 drawn from wide comparison would be directly antagonistic to such a 

 history. The young sporophyte of a Fern first forms foliage leaves, 

 stem, and roots ; only after a considerable period are sporangia pro- 

 duced. On the recapitulation theory it would' be concluded from this 

 that the vegetative system was the first to appear, while sporangia were 

 of subsequent origin, and it might further be held that sporophylls 

 are metamorphosed foliage leaves. But the whole comparative study 

 of the sporophyte of lower forms leads to the opposite conclusion ; 

 spore-production was the first office of the sporophyte, and if the 

 lower Bryophyta really illustrate the mode of origin of the sporo- 

 phyte, the production of spores preceded the existence of a vegetative 

 system of the sporophyte, and was apparently a constantly recurring 

 event throughout evolution. It must, therefore, be concluded that 

 the history of the ontogeny does not truly recapitulate the history of 

 descent as regards the neutral generation ; the sporophyte is, in fact, 

 an intercalated phase which has acquired vegetative characters. 

 Comparative study of the Bryophyta leads to the conclusion that the 

 whole vegetative region was the result of progressive sterilisation of 

 potentially sporogenous tissues. 



A brief review of the progress of this sterilisation as it has already 

 been recognised among the Bryophyta is next given ; it is pointed 

 out that (a) the sterilisation may involve the whole thickness of the 

 sporophyte, as in the formation of the seta, or (&) it may make itself 

 apparent only in individual cells of the sporogonial head (elaters). 

 It is important to note that Leitgeb concluded that in certain cases 

 the latter might be massed together to form solid tracts of sterile 

 tissue, such as the columella of the Anthoceroteaa. But though a 

 considerable degree of vegetative advance may be traced in the 

 Bryophyta, and correlated with progressive sterilisation, still they are 

 clearly marked from vascular plants by two characters: (1) the 

 absence of appendicular organs ; (2) the single continuous arche- 

 sporium. 



There are, at least, three possible ways in which plants with 

 numerous separate archesporia may have originated from plants of 

 the Bryophytic type : (i) by branching (chorisis) of a sporogonial 



