118 THE POLYSPORANGIATE STATE 
previously existent in the race: much less is this possible for the individual 
sporangia of those sori Such an example shows, in its most extreme 
form, how impossible it may be to compare, as numerically or locally 
identical, the otherwise similar parts, such as sori or sporangia: and 
this is most clearly so in the Ferns, where the leaves are large, and. the 
sori and sporangia borne upon them more numerous than in,any other 
Vascular Plants. 
We thus see that the homosporous Pteridophytes, which are certainly 
the more primitive, will be the best guide in questions of the origin of 
the sporangial state: and that these may be arranged serially according 
to size of the appendages, the strobiloid types being at one end of the 
series and the large-leaved Ferns at the other. The forms thus arranged 
show more or less clear differences in the sporangial characters: in the 
simpler strobiloid forms the sporangia are less definite units as regards 
spore-output, in the Ferns they have tended to, become in the evolutionary 
course more definite units in this respect. In the-strobiloid forms the 
relation of the sporangium to the axis is close, and as regards position 
and number it is more definite; in the larger-leaved forms the sporangia 
are further removed from the.axis, and their position and. number tends to 
become more and more indefinite. In the-strobiloid forms the time of 
origin of the sporangia in near juxtaposition to one another is simultaneous : 
in the larger-leaved forms it tends to become in various ways successive, 
while the palaeontological record shows that the most pronounced succes- 
sions have been of secondary origin. These distinctions will have their 
value in leading to a more precise statement of the problem of origin of 
the sporangial state. To this end it will be found desirable to keep 
distinctly before the’ mind those vascular types in which the nearest 
approach can be made to a comparison of the sporangia as numerically 
and locally identical. Among the homosporous Pteridophytes this will 
be found to be the case most nearly in the smaller-leaved ‘ strobiloid 
forms: and among these especially in the ancient phylum of the 
Lycopodiales. 
