EXCLUSION OF CERTAIN FACTORS 131 



occurred in various instances, and in any given case the proper initial 

 attitude is to hold that either mode of origin may have been the source 

 of the synangial state as it now appears. 



The feature which has probably been most effective of all in distracting 

 attention from the methodical analysis of the polysporangiate state in 

 Vascular Plants at large has been the swamping effect of continued apical 

 growth, and of branching. In the lower Vascular Plants both apical 

 growth and branching may be seen in either the sterile or the fertile 

 regions. In the higher Flowering Plants the floral region itself is 

 characterised by absence of branching, and by restriction of apical growth, 

 but both occur freely in the sterile region of the inflorescence. The 

 results of this in the Flowering Plants are apt to be so dominating that 

 it is often hard to recognise the small terminal and late-produced strobilus 

 or flower as the actual residuum which progressive sterilisation and growth 

 of the sterile tract have left. 



Among Vascular Plants it is only in the simpler Pteridophytes that this 

 aspect of the sporophyte generation clearly emerges : and this is largely due 

 to the fact that in them branching of the axis is often less profuse, or may 

 even be absent altogether : moreover, the structural similarity between the 

 sterile and fertile regions suggests their comparison. As a consequence of 

 such comparisons, it follows that the great disproportion of the two regions 

 so often seen in the Flowering Plants may be discounted as a secondary 

 effect : it has been brought about principally by continued apical growth 

 and repeated branching in the vegetative region, together with higher differ- 

 entiation of the sterile and fertile shoots. Maintaining consistently this 

 point of view, the overpowering effects of continued apical growth and of 

 branching will be estimated at their right value, and so the way may be 

 prepared for a more exact enquiry into the origin of the polysporangiate 

 state, even in the more advanced types. It is by some such analysis as 

 that sketched in this chapter that it may be possible to attain to a 

 reasonable opinion how the condition seen in the earlier Vascular Plants 

 came into existence. The detailed practical application of the method may 

 often be difficult, and only partially successful : the present object has been 

 to lay the basis for such an analysis, by showing what the recognised 

 factors of numerical change of sporangia actually are, and to simplify the 

 problem by showing that certain of those factors are of limited application 

 only. 



