224 Royal Society: — 



any of the others described. Two of the extremities of the crucial 

 arms of the vascular bundle become first enlarged and then detached 

 as two secondary bundles, which generally have an irregularly 

 triangular transverse section, with long arms to the triangle. 

 These triangular bundles are altogether different from the central 

 axis of Asteropliyllites described in a preceding memoir. The 

 ultimate subdivisions of these secondary branches look more like 

 the terminations of cylindrical rootlets than of petioles — which fact, 

 combined with the circumstance that no traces of leaflets have been 

 found associated with any of these ultimate twigs, renders the 

 petiolar nature of this plant open to question, though the argu- 

 ments in favour of its being a branching fern-petiole preponderate 

 over those which militate against that conclusion. The author 

 designates this plant Machiqpteris Oldhamia. 



The next plant described is an exquisitely beautiful petiole from 

 Burntisland, to two detached portions of which the author has 

 already assigned the names of Arpeccylon duplex and A. simplex* ', 

 but which two forms he now proves to belong to the same plant. 

 In the matured petiole the vascular bundle is always a double one. 

 There is a central bundle, exhibiting a transverse section shaped 

 like an hour-glass, one side of which is truncated and the other 

 rounded, with a free, narrow, crescentic band at the more truncate 

 of its enlarged extremities. At each of these extremities of the 

 central bundle there is a longitudinal groove, which is shallow on 

 the truncated side nearest to the crescentic bundle, but so sur- 

 rounded by small vessels at the opposite convex side as often to 

 become converted into a longitudinal canal. The hour-glass bundle 

 always reappears in various specimens under the same aspect ; but 

 the crescentic one divides into two lateral halves, and the ends of 

 each of these two subdivided parts curl under their more central 

 portions. We thus obtain two of the crescentic structures pre- 

 viously designated Arpexylon simplex. These crescents are traced 

 outwards through the bark to lateral secondary raches. The vessels 

 thus detached from the truncated side of the central hour-glass 

 bundle now reappear at its opposite and more convex side, whence, 

 in turn, they again become detached ; so that the truncate surface 

 with its crescentic appendage, and the more oblate one with its 

 almost closed canal, have alternately reversed their positions in 

 the petiole as each secondary rachis was given off. Alternating 

 distichous tertiary raches spring from these secondary ones. 



Two plants which appear to be identical with those described 

 by M. Renault, under the names of Zygopteris Lacattii and Z. bibrac- 

 tiensis, are next examined t. In these plants the section of the 

 central bundle exhibits a form of the letter H. The vessels of the 

 large central transverse bar are all reticulated ones : the greater 

 part of those of the terminal vertical bars are of the same cha- 

 racter ; but the outermost vessels of those latter structures are 



* Proceedings of the Koyal Society, vol. xx. p. 438. 



t Annales des Sciences Naturelles, 5 e serie, Bot. tome xii. 



