n8 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. 



