4io 



SPHENOPHYLLALES. B. PSILOTACEAE 



unbranched, though occasionally a dichotomy may be observed (Fig. 226 A). 

 The aerial shoots differ from the rhizomes in bearing appendages : first, 

 small scale-like bodies are produced, but higher up they enlarge gradually, 

 till the condition of the fully-formed foliage leaf is attained : this is about 

 half an inch, long, and flattened in a vertical plane. The basal vegetative 

 region is continued directly into the fertile region : here the distinctive 

 feature is the forked sporophyll, 1 which bears the sporangiophore seated 

 at the fork, and on its adaxial surface : each sporangiophore supports 

 two large and confluent sporangia (Fig. 226 B, c). The disposition of 

 the leaves upon the mature axis is irregularly alternate, and this appears 

 in transverse section of the apical bud (Fig. 227) : here the axis shows 



FIG. 227. 



Transverse section through a spor- 

 angiferous bud of Tmesipteris. ax = 

 axis. , y=foliage leaves. I lateral 

 lobes, .y^synangia. X2o. 



FIG. 228. 



Tmesipteris tannensis, various unusual forms 

 of sporophyll and sporangiophore ; in i. thesyn- 

 angium is abortive ; in ii. and iii. one loculus is 

 abortive ; others show a larger number of loculi 

 than two ; others again, right and left on the 

 lower row, show a single loculus, the septum 

 being imperfect, or absent. 





a very irregular outline owing to the decurrent bases of the appendages : 

 it is also apparent that these are alternate : it may also be noted that 

 in the case figured three foliage leaves (/) are inserted above the three 

 sporophylls (/, sy, /). 



The fertile region forms a very lax strobilus, in which the following 

 features may be noticed. It does not differ markedly from the vegetative 

 region in the size of the parts which it bears : it is not composed exclusively 

 of sporophylls, but foliage leaves of the usual type may be interspersed 



1 The terminology here used is that of Scott (Stttdies, p. 479). I regret having in 

 1893 (Sttidies, part i.) used the term sporangiophore in a wider sense than here, so 

 as to include the bifid sporophyll itself. Such an extension of the term obscures the 

 natural comparisons not only with the Sphenophylleae, but also with other sporangio- 

 phoric types. It is best to restrict the use of the word in the Psilotaceae to the 

 body borne by the bifid sporophyll, often designated also the synangium. The various 

 opinions previously held as to the morphology of these appendages need not be discussed 

 again here. It will suffice to refer to my Studies, i., p. 539, where they have been 

 considered at some length, with references to the literature relating to them. See 

 also Lignier, Bull. Soc. Linn, de Normandie, 1904, p. 95, and footnote. 



