FILICES. 



161 



accordingly altered Brongniart's name into Myelopteris ; he also endea- 

 voured to prove l that these leaf-stalks belong to Alethopteris aquilina 

 which is so common a species at Grand' Croix. Since that time no further 

 doubt has been openly expressed with respect to the nature of these re- 

 mains, though Schenk 2 has lately contended that they are the leaf-stalks 

 of Cycads and not of Ferns. If I discuss them here with Ferns, it is 

 entirely from motives of convenience and after frequent examination of 

 specimens in my possession ; decisive proof of one or the other view 

 appears to me to be still wanting. 



The cylindrical leaf-stalks of Myeloxylon 3 (Fig. 14) I use this name 

 rather than Stenzelia because it is better known are of unusually varying 



FIG. 14. Transverse section of leaf-stalk of Myeloxylon. A synoptical view showing the subepidermal fibre-strands, 

 the vascular bundles, and the gum-passages. B transverse section of a single bundle with phloem preserved. A after 

 Renault, B after a preparation in my collection. 



thickness ; I have some before me with a diameter of seven, eleven, "and 

 sixty millimetres, and Renault has figured some that are much thicker. 

 Their uniform parenchymatous fundamental tissue encloses a large number 

 of vascular bundles, which though not quite regularly disposed yet form 

 numerous concentric circles. There are also many gum-passages, which 

 are filled as a rule with some dark substance, and may be known by the 

 usually well-preserved epithelium. A rather broad subepidermal zone is 

 quite filled with one or more rows of crowded radiately disposed scleren- 



1 Renault (2), vol. iii. 2 Schenk (9). 



3 The latest observations have made it probable that the Myeloxyla are the leaf-stalks of the 

 Medullosae described on p. 103. The owner of the precious bit of Medullosa Leuckarti mentioned 

 there has recently had the lateral branch cut through transversely, and the section seems really to 

 show the structure of Myeloxylon, as far as can be determined without examination of thin slices. 

 If this unexpected find is confirmed by further investigation, a new and important weight will be 

 added to the scale on the side of Cycadeae. I am indebted to Herr Leuckart's kindness for my 

 knowledge of the specimen in its present state. 



M 



