262 HOFMEISTER, ON 



botanists are now unanimous upon all the essential points 

 of the question. 



The anatomy of the stems of ferns (the course of whose 

 vascular bundles had been supposed to be very similar to 

 that of the monocotyledons) was first clearly explained by 

 H. v. Mohl (de structure, caulic. filic. arbor, in v. Martins' 

 Icon, plant, cryptog. Brasil. Munchen 1835 ; translated in 

 H. v. Mold's ' Vermischte Schriften/ p. 108). He pointed 

 out that the closed vascular bundles (which do not increase 

 in thickness after they are first formed) in tree ferns as well 

 as in the herbaceous species form a hollow cylindrical net 

 concentric with the periphery of the stem, whose meshes, in 

 the species with crowded fronds (dsj)lfilix-mas for instance), 

 are arranged with the greatest regularity in the following 

 manner, that is to say ; from the place where each frond is 

 attached to the cylinder, two bundles pass to the bases of 

 the two next higher fronds, and two to the bases of the two 

 next lower ones. This regularity in the relation between the 

 anastomoses of the vascular bundles and the places of in- 

 sertion of the fronds, does not occur in the species with 

 distant fronds, such as Polj/podium aureum. The difference 

 between the tree-ferns and the herbaceous species is im- 

 material, depending upon the breadth of the vascular 

 bundle, and the development of the sheaths of the latter out 

 of woody prosenchyma. At the place where a vascular 

 bundle passes into a frond an entire bundle is never found to 

 bend itself outwards for that purpose, as is almost always 

 the case in phaenogams, but small ramifications only are sent 

 off into the fronds.* Later observations have not yielded 

 any additional results of importance. 



Brogniart first made known that the ramification of the 

 stems of ferns is caused exclusively by bifurcation of the 

 extremity (' Histoire des vegetaux Fossiles,' ii, p. 30), an 

 opinion which has been supported by Stenzel (' Jahresb. 

 Schles. Ges.,' 1857, p. 85), and by myself. f On the other 



* Unger's notion of the ferns and their allies as " Plantce acrobryce " is founded 

 upon this important peeularity (' Unger Bau und Wachsthum der Dikotyle- 

 donen-stamen/ Petersburg, 1840; ' Anat. und Physiol, d. Pfl.,' lS50,p. 225). 



f My observations on this subject which are given in the preceding pages 

 were first published in the Transactions of the Royal Society of Sciences 

 of Saxony, vol v, p. 60. 1857. 



