84 BOTANICAL GAZETTE [july 



under which these epiphytic species grew are described as being 

 about the optimum for vegetative growth. A definite structural 

 evidence for rapid elongation in these plants is the close series in 

 sporogenesis shown by serial transverse sections of the strobilus. 

 It would seem then that these variations of stelar structure occur 

 under conditions favoring rapid elongation. Whatever the con- 



may be, the fact of the variations em 



elopment 

 i fixed str 



) moc 

 most 



Summary 



i . From this investigation it may I 



Lycopodium studied are character] 



development and structure of the 



great variability in 



2. The radial stele may be considered as the prevailing 



• 



most cases for modification 



found. 



3. There are found radial, parallel-banded, crescentic, and 



and 



amphivasal steles in the same strobilus axis in L. carmatum, 

 all types but the amphivasal in L. Phlegmaria and L. varium. 



4. L. Billardieri is the most constant in its stelar structure, 

 with a type of stele so characteristic as to make the species almost 

 recognizable by the transverse section of the stem. 



5. L. verticillatum has generally parallel-banded arrangement 

 of stele, although the radial stele has been considered the prevailing 

 type in epiphytic species. 



6. All attempts to place the species of Lycopodium in definite 

 categories based on the character of the stele are extremely uncer- 

 tain, since there are exceptions in some species and even exceptions 

 in different parts of the same stem in some species. 



7. If the character of the stele is in any way dependent upon 

 varying conditions, its use in phylogeny must recognize this fact. 



8. The investigation confirms the idea that the radial arrange- 

 ment of the stele, retained persistently by the root, is probably 

 the most primitive stem arrangement, from which most known 

 stems have deuarted. 



