GENERAL MORPHOLOGY 



409 



between them, as well as the variations in the individuals in either genus, 

 afford an important basis for 

 comparison with other forms, 

 throwing light upon fluctuations 

 of structure which would other- 

 wise be more puzzling than 

 they now appear to be. 



Both genera are rootless. 

 The green, more or less shrubby 

 shoot, is established in the 

 substratum, which is usually of 

 humus character, by means of 

 a plexus of leafless rhizomes 

 invested with rhizoids, and 

 penetrated by a mycorhizic 

 fungus. The nutrition of these 

 plants is thus of a mixed char- 

 acter, partly saprophytic, partly 

 by photosynthesis. The aerial 

 shoots bear appendages of two 

 sorts, described as foliage leaves, 

 which are simple, and sporo- 

 phylls, which are forked. These 

 may be associated together 

 irregularly on the same shoot 

 which thus takes the character 

 of a lax, undifferentiated stro- 

 bilus. 



In Tmesipteris, of which the 

 single species T. tannensis is 

 native in Australasia, though 

 extending northwards to the 

 Philippines, the structure is 

 more simple than in Psilotum. 

 Its habit is peculiar, the plant 

 being established on the trunks 

 of tree-ferns, though occasion- 

 ally it has also been found 

 growing upon the ground. 



, . . . . Tiiifsipteris tannensis, Bernh. si = Habit-figure of a whole 



1 he rhlZOme, Which fixes It in plant (pendent form), showing a dichotomy. Natural size. 



, , . B-E, sporophylls, with synan^ia : />', seen from the side; C, 



the SUDStratum, IS repeatedly from above; A after dehiscence; .ff, from the under (dorsal) 



i , , j-i side, allxabout 3. ./^rhizome \A natural >ixe. 6" = trans- 



brancned 111 a dlChotOniOUS verse section of old stem, x 4. (After Pritzel in Engler and 



, . , Prantl, *Vai. Pflanzenfam.) 



manner and is without appen- 

 dages other than rhizoids. Branches of this system turn upwards to the 

 light, and develop as the aerial shoots : these are usually themselves 



D 



FH;. 226. 



