THE POLY-SPORANGIATE STATE 249 
also probably primitive and certainly early, the appendages are larger, and 
the sporangia more removed from the axis; and in proportion as this is 
so their number is less precise. But even where the appendages are 
largest, as in Ferns, or Ophioglossaceae, the relation of leaf to axis remains 
essentially the same. 
The variations of number of sporangia actually seen as effective in 
Vascular Plants have been discussed in Chapter X., in which methods of 
increase are separated from those of decrease. Both of these are liable 
to be disguised by the swamping effect of continued apical growth, and of 
branching of axes and appendages, which are so prevalent in Vascular 
Plants. But, putting these more obvious sources of numerical change of 
sporangia aside, there are others which have also been effective, and have 
probably played an important part in evolution. As factors of increase in 
number of sporangia septation and interpolation are to be recognised. 
The former of these has probably been underestimated hitherto in its 
evolutionary effect: numerous synangial bodies in Pteridophytes are com- 
patible with it, and each must be considered on its merits; moreover, 
septation is demonstrated to have actually occurred in the anthers of a 
number of Angiosperms. Interpolation of new sporangia among those 
previously present, on the other hand, has hitherto been overestimated : 
in certain of the simplest forms, and particularly in the Lycopods, it is 
non-existent: it is more prominent in larger-leaved forms, where sporangia 
are indefinite in number, such as the Ferns, and it has played an 
important part among the later Polypodiaceae; but no clear case of it 
is known among Palaeozoic Plants. It is held as a relatively late mode 
of increase, initiated as a secondary phenomenon, and it cannot be 
assumed to have been of general occurrence in the course of descent. 
Among the factors of decrease in number of sporangia the arrest of 
apical growth in axes, or in appendages, has probably been one of the 
most effective, and especially so in the later types of development; but 
as this, where operative, would leave no trace behind of what had actually 
occurred, it is liable to be underrated in its effect. The chief remaining 
factors of decrease are fusion of sporangia originally distinct, and abortion. 
The former of these has probably been overestimated hitherto in its 
evolutionary effect: the assumption has been too generally made that 
synangia are the result of fusion of sporangia originally separate. Each 
such case must be considered on its merits, but with the full conscious- 
‘ness that septation will produce results structurally similar to those of 
fusion. Abortion has been altogether underestimated in dealing with 
early Vascular Plants. In the Lycopods there is ample evidence of its 
effect; and it is to be remembered that where abortion is complete, 
no vestige remains to show what has taken place (Chapter XIII.). 
The condition of any poly-sporangiate sporophyte, regarded from an 
evolutionary aspect, may be held to be the resultant of such conflicting 
factors of increase or decrease as those mentioned, which were operative 
