PHANEROGAMIA : AXIAL ORGANS. 245 



and run together in a horizontal direction below the rind, from both sides 

 up to the buds. On cutting vertically through one of these stems, we find 

 a transversely severed, strikingly large group of vascular bundles below 

 the rind, corresponding to each internode. It unfortunately happens with 

 the Orchidacece, as with the Cacti, that it is a matter of difficulty to obtain 

 a sufficient quantity of material to ascertain the anatomy or its history of 

 development. 



D. DICOTYLEDONS. 

 I. Stalks. 



The stalks frequently exhibit no essential differences from those apper- 

 taining to Monocotyledonous plants, since the distinction of the unlimited 

 or indefinite vascular bundles is often imperceptible in the growth of one 

 year. But the vascular bundles generally close in the first year into a 

 simple circle, and the external parts in several circles to form a ring, so 

 that the parenchymatous masses separating the individual bundles are 

 compressed together into medullary rays. In most cases thej vascular 

 bundles run from below upward in straight parallel lines. They form a 

 loop where the leaf begins, the edges of which furnish vascular bundles 

 for the leaf and the axillary bud, and the pith of the bud is thus brought 

 in connection with that of the stem by means of their opening, as in the case 

 of Tropceolum. THe vascular bundles supplying the leaves and buds gene- 

 rally separate from this loop exactly at the point where they enter the 

 leaf. Sometimes, however, they first pass through a longer portion of the 

 parenchyma of the pith or the bark (as in the Amaranthacece and Cheno- 

 podiacce).* In perfect nodes, loops of vascular bundles are seldom found 

 passing across the stem ; in general the parenchyma merely appears to be 

 tougher and closer at these points. We are here, on the whole, very 

 destitute of accurate investigations, more especially with regard to the 

 first year's stalk with undeveloped internodes. 



II. Stems. 

 1. Developed Internodes. 



A. With a simple Ring of vascular Bundles. 



Here the vascular bundles very seldom run parallel, but generally in 

 serpentine lines, alternately approximating and retreating from each 

 other ; the meshes thus formed are filled by the medullary rays. Where 

 liber-bundles lie in front of the vascular bundles they follow the same 

 course. f Large and small medullary rays, and annual rings, are formed in 

 the manner indicated. Wherever there is a leaf, one large or several 



* Very admirable observations on this last-named point may be found in Unger, 

 Bau, &c., des Dikotyledonenstammes, Petersburg, 1840. 



f In this manner is formed that beautiful network which used formerly to serve the 

 West Indian beauties as a natural lace veil, and which was derived from Daphne Laaetta 

 (Palo di Laghetto, Lace bark tree, Bois de dentel/e). 



