29<5 PRIMARV ARRAyGEMENT OF TISSUES. 



described for the Polypodiacese with a reticulately divided lower bundle, having long 

 narrow, rather irregulai meshes : foliar meshes and points of origin of lateral shoots 

 appear only in regular alternation, on both sides of a clearly distinguishable upper 

 bundle. Outside this net is a peripheral one, showing in transverse section fifteen 

 to about fifty bundles, which rarely form a single circle, but are usually arranged at 

 the upper side of the stem in 2-3 irregular series, at the lower side of the stem in a 

 curve. The bundles of the perijiheral net are thin and connected in elongated 

 meshes, in the arrangement of which there w'as as litde regularity to be recognised as 

 in that of the obliquely ascending connecting-bundles, by which the outer net is 

 joined with the inner at many points. Three branches arising from a single mesh 

 of the inner net and 9-12 peripheral ones enter each lateral shoot; into the base of 

 the leaf there pass two or several inner, and 9-24 outer ones. All roots arise from 

 the outer net. 



c. Bundle system in the leaves and foliar expansions. 



Sf.ct. 88. The bundles, which leave the bundle-cylinder of the stem and pass 

 out into the leaves, run as a rule towards the margin and apex of the leaf. 



The bundles may run from their point of departure from the cylinder of the 

 stem onwards, just as they did in the latter, as for instance in a leaf of a Conifer, where 

 one bundle passes out from the cylinder and runs without division up to the apex of 

 the leaf; or divisions of the bundles and coalescences of separate ones may occur at 

 any point, so that the number to be seen in the transverse section of the leaf is not 

 the same as at the point of exit itself. Examples of this, when it takes place in the node 

 itself, have been given above, Sect. 61 ; in the case of their further course the pheno- 

 menon is universally known, and will be treated in detail in the following paragraphs. 



In most cases the bundles at the nodes pass, without division, or after splitting 

 into branches which run side by side, through the cortex into the leaf But in certain 

 individual cases there appear special branches at the node itself, which lie in the 

 parenchyma of the cortex ; these are here connected into a net or a transverse 

 girdle ; often branch bundles pass downwards from the node into the cortex of 

 the adjoining internode. 



Branches peculiar to the node (which do not pass out from it) are often found 

 where several bundles emerge, forming oblique or curved connections between these. 

 This is the case both in many traces with numerous bundles, belonging to solitary 

 (alternating) leaves, e.g. Lathyrus Aphaca (comp. p. 240), where the median bundle 

 has a curved transverse connection with the lateral ones ; Viola elatior, Platanus, 

 which will be mentioned below : also in whorls of two or more with leaves having 

 one or more bundles. In the case of leaves with one bundle Hanstein ^ found a 

 transverse girdle connecting the bundles at the node in numerous Rubiaceae with 

 whorls of two or more members (species of Asperula, Rubia, Galium, Hamelia 

 chrysantha, Houstonia coccinea, Bouvardia mollis) ; on the other hand, other Ru- 

 biaceae (Coprosma ligustrina, Exostemma floribundum according to Hanstein) show 

 no transverse girdle. In whorled leaves with several bundles transverse girdles have 



* Ueber gurtelforniige Gefassstrangverbindnngen, Abhandl. d. Berliner Academie, 1857, P- 77- 



