290 LYCOPODIALES 



are disposed in radiate fashion around its distal end, which is usually 

 enlarged. The whole structure, which is called a " sporangiophore," may 

 be inserted directly on the axis, as in the Equisetales, or upon the appen- 

 dages of the axis, as in the Sphenophy Hales (including the Psilotaceae). In 

 the latter case the position is, as a rule, in the median plane of the 

 subtending leaf; but in cases where the sporangiophore is more elaborate 

 and shows indications of branching the position may be less obvious. 

 Extreme elaboration of the sporangiophore, sometimes including its branch- 

 ing, is seen in the series of the Ophioglossale-s, which appear as the most 

 advanced examples of this pedicellate or Sporangiophoric Type. 



In a third series, the Filicales, the sporangia are usually grouped in 

 " sori," which have features in common with the sporangiophores, but they 

 differ from the sporangiophoric types in that the sori are distributed over 

 the margins or surfaces of the leaf itself, which is here of relatively large 

 size and complex construction. 



The order of description will follow the sequence thus laid down, and 

 it will become apparent that the elaboration of the leaves themselves 

 follows roughly parallel with that of the sporangial arrangement : in fact the 

 whole series may be regarded as progressing from simpler to more complex 

 types of the whole shoot. The arrangement thus adopted is convenient 

 for description. The question will be reserved for later discussion how far 

 it indicates a true evolutionary progression. 



LYCOPODIALES. 



/. General Morphology. 



These plants are taken first because in them the spore-producing members 

 are more simple and regular in their disposition on the shoot than in any 

 other Vascular Plants. Throughout this phylum (as now limited by the 

 exclusion of the Psilotaceae), each single sporangium is subtended by a 

 sporophyll (Frontispiece), the median planes of the sporophyll and of the 

 sporangium coincide, and typically no more than one sporangium is 

 associated with each sporophyll. 1 These appendages are borne laterally 

 upon the axis, which is endowed with apical growth. The arrangement 

 of the appendages, either sterile or fertile, is sometimes in regular 

 whorls, but frequently it is according to some more or less interrupted 

 spiral scheme (Fig. 141). The axis may undergo frequent branching, 

 typically in a dichotomous manner, though intermediate steps are seen 

 in certain species to the monopodial type : in some of the Lycopodiales, 

 however, branching is rare, or absent. It is thus evident that the whole 

 shoot is of a simple strobiloid type. It bears roots at its base, and in the 



1 Occasional exceptions have been noted, where two small sporangia, side by side, are 

 subtended by a single sporophyll. These are rare, and appear to originate in some form 

 of fission of the normal sporangium (Annals of Bot., xvii., p. 278). 



