POSITIVE DEDOUBLEMENT. 101 



here once more a structure which is the homologue (to 

 cite one instance) of the petal- enations of Narcissus. 

 In that plant, as showing that the ventral excrescence 

 or corona really represents the fusion of two lateral 

 lobes of the perianth-leaf, Celakovsky observed and 

 figured perfectly petaloid stamens provided with a 

 lateral lobe on each side which had the exact consist- 

 ence, colour, and form of the corona. Now, just as the 

 petaloid enations of Narcissus may equal in develop- 

 ment the leaf which bears them, in the same way do 

 the fertile " spikes" of Botrychium and Helminthostachys 

 equal in size and elaboration the sterile portion of the 



F 



Fig. 111. — Psilotum triquetrum. Plurisporangiate sporophylls. 

 (After M. G. Sykee.) 



frond which bears them. (Conversely, the sterile 

 lamina, as seen by Hergt in Ophioglossum vulgatum, 

 may be abnormally lobed, after the manner of that of 

 Botrychium, ; probably a reversion.) 



In the Psilotaceas the sporophylls, normally exces- 

 sively reduced in their conformation, may abnormally 

 become rather more complex. A. P. W. Thomas 

 describes most interesting cases in Tmesipteris ; the 

 normal sporophyll is forked, and bears at the point of 

 forking a single synangium. The abnormal ones are, 

 however, repeatedly forked, and the synangia corre- 

 spondingly increased in number. In other cases the 

 synangium is raised up on a distinct stalk of its own. 

 He also mentions, and Miss Sykes describes in detail, 

 abnormal sporophylls of Psilotum which are repeatedly 

 bifurcated in a similar way, with a great corresponding 



