ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 875 



of the veins, and therefore varies according to the part of the leaf 

 where the section is made. 



Each bundle includes a small band of woody tissue, usually flat- 

 tened and surrounded on all sides by a thin layer of liber-elements. 

 In the deeply incised lobes of the leaves the woody tissue forms, on the 

 contrary, a small circular mass in the centre of the liber. It is com- 

 posed of from five to twelve extremely slender tracheae. The liber- 

 elements are in direct contact with these ; they are slender tubes with 

 very thin walls. The liber-elements compose one or two layers ; their 

 thickness is less on the exterior than on the interior face of the 

 woody bundle. 



The vascular bundle never consists of any further elements than 

 these. There are neither centripetal ligneous elements nor an 

 external formative zone, nor secondary wood or liber. It is sur- 

 rounded by a layer of larger cells with thin walls, which separates it 

 from the mass of the fundamental tissue ; it is uncertain whether this 

 layer is of the nature of a sheath. 



The fundamental tissue is composed of large rounded cells with 

 thin walls, and a number of passages between them ; in the neighbour- 

 hood of the vascular bundles a portion of this tissue is differentiated 

 into a hypoderma. Each bundle is in fact placed between two strings 

 of hypodermal bundles ; one superior, consisting of from six to fifteen 

 bundles, and stretching from the vascular bundle to the upper 

 epidermis ; the other inferior, and extending from the vascular bundle 

 to the lower epidermis. There is no break of continuity between 

 the epidermis and the hypodermal bundles, nor between the elements 

 of the hypodermal elements, nor between them and the vascular 

 bundle. 



The upper epidermis consists of cells somewhat rounded on trans- 

 verse section, with thick walls and somewhat larger in the direction of 

 the veins ; the lower epidermis of cells with vertical walls, also 

 somewhat rounded, but smaller, and in direct contact with the hypo- 

 dermal bands. 



The vascular bundles of the leaf of Sphenophyllum have therefore 

 no centripetal woody tissue, and therefore no power of centrifugal 

 secondary growth ; their structure is that of the very small bundles 

 of the leaves of vascular cryx^togams ; and no conclusion can therefore 

 be drawn from their structure favourable to the alliance of Splieno- 

 phyllum with the Sigillarias. 



Structure of Phylloglossum.* — C. E. Bertrand states, as the 

 result of an examination of Phylloglossum, Drummondii, that the fertile 

 peduncle is an axis, since it presents several lines of symmetry passing 

 through one point ; that the woody mass of this peduncle represents 

 three bicentral bundles ; and that the masses diametrically opposed to 

 one another are united like the woody masses of a bicentral bundle of 

 Lycopodium, Selaginella, and Tmesiptei-is ; that, in consequence, the 

 peduncle is a stipes ; that this stipes differs from the fertile stems of 

 Lycopodium only by the presence of three bundles instead of two ; 



* Comptes Rendus, xcvii. (1883) pp. 504-7, 612-5, 715-7. 



3 N 2 



