CHAPTER XII. 



SPORANGIOPHORES AND SPOROPHYLLS. 



THE theoretical position taken up in the last chapter is characterised not only 

 by its simplicity but also by its elasticity. It carries with it no obligation 

 to assume that all the appendicular organs should show definiteness or 

 constancy in their disposition upon the axis which bears them, nor even 

 that they were all alike in their initial character or function. Now, as a 

 matter of fact, an examination of the strobili of such plants as the Psilo- 



taceae, Horsetails, and Calamarians shows that 

 irregularities of arrangement of the parts are 

 common : it is impossible to reduce the 

 arrangement of the appendages in the cone of 

 Tmesipteris or of Eijitisctnm maximum to any 

 regular scheme (Fig. 73) : the appendages of 

 both vary in radial angle and in level of 

 insertion. There is also great variability in 

 the disposition of the leaves in the genus 

 Lycopodium, being sometimes whorled, some- 

 times irregularly spiral. It is true that cases 

 do exist among the strobiloid Pteridophytes 



I i inverse section through a sp<>T- . . . . . .... - 



angiferous bud of TmesipKris. ax= which show regularity in the disposition ot 



axis. /= foliage leaves. /=lateral . ... . 



lobes. jy=synangia. X2 O . their parts, but in their shoots at large a 



regular disposition of the appendages cannot 



be held to be a general feature. Such irregularities, so far as they are 

 of primary origin, are difficult to explain on the basis of any sympodial 

 construction of the strobilus : to a theory of enation, as expounded 

 in the previous chapter, they offer no obstacle ; for if the appendages 

 originated from the surface of the pre-existent axis, as suggested, they 

 might equally well appear in regular positions, or be disposed with greater 

 or less irregularity as, indeed, is seen to be the case. 



The comparative classification of those appendages of the strobilus 

 which are seen in the different types of Pteridophytes has always presented 



73. 



