620 
Notes . 
II. Decrease in Number of Sporangia. 
(/) By fusion of sporangia originally separate. 
(g) By abortion, partial or complete, of sporangia. 
(k) By reduction or arrest of apical or intercalary growth in parts 
bearing sporangia. 
(i) By fusion of parts which bear the sporangia or arrest of their 
branchings. 
(J) Indirectly, by suppression of branchings in the non-sporangial 
region, resulting in decreased number of sporangial shoots ; 
this is closely related to ( h ) and (i). 
We are justified in assuming that (subject to the possibility of 
other factors having been operative, of which we are yet unaware) the 
condition of any polysporangiate sporophyte as we see it is the 
resultant of modifications such as these, operative during its descent. 
The problem will, therefore, be in each case to assign its proper 
place in the history to any or each of these factors. 
It is pointed out that in homosporous types, which are certainly 
the more primitive, the larger the number of spores the better the 
chance of survival, and hence, other things being equal, increasing 
numbers of spores and of sporangia may be anticipated ; but in the 
heterosporous types reduction in number both of spores and of 
sporangia is frequent. The former will accordingly illustrate more 
faithfully than the heterosporous forms the story of the increase of 
complexity of spore-producing parts. The general method put in 
practice here is to regard homosporous forms as in the upgrade of 
their evolution, as regards their spore-producing organs, unless there 
is clear evidence to the contrary. The onus probandi lies rather 
with those who assume reduction to have taken place in them. 
A summary of evidence of variation in number of sporangia by 
any of these methods is then given for the Lycopodineae, Psilotaceae, 
Sphenophylleae, Ophioglossaceae, Equisetineae, and Filicineae; followed 
in each case by a theoretical discussion of the bearing of that evidence 
on the morphology of the spore-producing members. The general 
result is that all of them, including even the dorsiventral and 
megaphyllous types, are referable to modifications of a radial strobi- 
loid type ; progressive elaboration of spore-producing parts, followed 
by progressive sterilization, and especially by abortion of sporangia 
in them, of which there is frequent evidence, together with the acquire- 
