BUNDLE-SYSTEM IN THE LEAVES. 30I 



Kne. The leaves of the broad-leaved Araucarias, and of species of Dammara and 

 Nageia, have more than two bundles, which run unbranched from the base towards 

 the apex, and end some of them at the apex, others below it. In Ginkgo the two 

 bundles which pass from the petiole into the lamina, branch repeatedly into 

 marginally directed forks. On Phyllocladus compare Strasburger, /. c. 



The pinnae of Cvcas contain one median bundle, those of most Cycadeae 

 numerous unbranched bundles, which run parallel or slightly curved from the base 

 to the apex. In Stangeria they are traversed by one middle nerve, in which 6-8 

 bundles run side by side ; these give off branches laterally, which are arranged in a 

 pinnate manner, and sometimes curve tow^ards one another and anastomose close to 

 the margin \ 



The leaves of Gnetum have, as far as is known, a typical reticulate bundle- 

 system ; in the leaf of Welwitschia there is a peculiar arrangement, which will be 

 described below. 



Among the Pteridophyta, besides the Equiseta already referred to, may here be 

 cited the awl-shaped leaves of Pilularia, Isoetes, Lycopodium, and Selaginella ; also 

 the leaves and portions of leaves with fan-like, dichotomous, branched bundles, 

 representing the Cyclopteris-nervation (e. g. Adiantum, Marsilia), and those with 

 bundles branched once or repeatedly in a pinnate manner, all being disconnected 

 and marginally or apically directed, which compose the nervation of Caenopteris, 

 Ctenopteris, Pecopteris, Taeniopteris, Sphenopteris, Eupteris, and Neuropteris ^ 



2. The foliar expansions with anastomosing bundles may be divided according 

 to the arrangement of the latter into two subordinate types, w^hich may be termed 

 the striated and reticulate. 



(a) In the striated type numerous bundles run separately and parallel along the 

 leaf- expansion, the median ones running straight to the apex, the rest diverging the 

 more from this straight course the nearer they are to the margin, and the more the 

 boundary lines of the latter depart from parallelism. Most of these bundles curve 

 towards one another close to the margin, and unite so that each one affixes its acro- 

 sropically-curved end on the basiscopic side of the one next it in the direction of the 

 median line. Free ends are rare. Throughout their course the bundles are con- 

 nected in a ladder-like manner by thin transverse branches. The former bundles 

 may accordingly be called shortly longitudinal bundles, in contradistinction to the 

 transverse branches. This arrangement is found, as far as is known, almost 

 exclusively in the Monocotyledons and in the leaves of the majority of their 

 families, also in the phylloclades of Ruscus and INIyrsiphyllum, in the latter cases with 

 transitions to the reticulate form. Some few families of Monocotyledons, such as 

 the typical Aroideae, Dioscoreae, Taccacese, and many Smilaceae, are exceptions. Of 

 plants which are not Monocotyledons, the leaves of Welwitschia and of many narrow- 

 leaved species of Eryngium, as E. pandanifolium, E. junceum, &c., belong to this 

 category, or are at least allied. 



According to the course of the longitudinal bundles we may. here again 

 distinguish two subsidiary forms, which are it is true connected by intermediate 



' Krans, in Pringsheim's Jahrb. IV. /. c. 



'^ Compare Mettcnius, Filices Horti Lipsiensis, p. 2, &c. 



