SPORE-PRODUCING MEMBERS 327 



there is thus evidence of great fluctuation in size of the sporangia, and 

 though the presence of the sterile trabeculae indicates that the limits of 

 convenience as regards nourishment and mechanical support are approached, 

 still there is no evidence that within the Lycopodinous phylum (as now 

 limited by the exclusion of the Psilotaceae) any actual septation has 

 occurred. The relation of one sporangium to each sporophyll, and no 

 more, is maintained throughout with some rare exceptions, which as they 

 never became characters of a race may be held as abnormalities. There 

 is, moreover, no evidence of interpolation of sporangia, those which exist 

 are all found to arise in strictly acropetal order. 



Finally, it would seem probable that the heterosporous condition, where 

 it occurs, supervened after the individual sporangia had already acquired 

 approximately the dimensions and characteristics seen in the different types 

 in which it appears. 



