ANOMALOUS THICKENING IN DICOTYLEDONS AND GYMNOSPERMS, 597 



extrafascicular cambial ring {c), which is somewhat more external, and consists for the 

 most part of a single layer, becomes visible : it is sharply distinguished from the paren- 

 chyma in- and outside it (which has meanwhile become large-celled) by the small size of 

 the transverse Section of its cells. If we first consider the longitudinal course of the 

 new bundles, which become visible at the same time as the cambial ring, and of those 

 which appear rather later and will be treated of subsequently (Fig. 234 a), they pass per- 

 pendicularly through the internode, being arranged in one or two circles outside the 

 bundles of the leaf-trace, and with out any quite definite position relatively to the latter. 

 In the nodQ limiting the internode above and below they are inserted on the outgoing 

 lateral bundles of the trace, and are also connected at once one with another by a 

 curved transverse anastomosis. Later, this insertion is obscured by the appearance 

 of very numerous connecting branches at the node. 



Fig. 234. 



F'S- =3S- 



Fig. 234,— Mirabilis Jalapa. Seedling, first and second epicotyledonary nodes ; above the latter is the growing point 

 with the third pair of leaves just beginning to appear, and' seen through the base of the leaf which is opposite the 

 observer. The preparation was made transparent by potash and glycerine, and consists of one longitudinal half,seen 

 from without, and with the vascular bundles drawn in. :>»i median bundles of the leaves of the first pair ; f»3 median 

 bundle of the nearer leaf of the second pair; l\, /a lateral bundles of the trace of the first and second pairs of leaves; 

 •v united bundle of the trace ; a, a secondary, apparently medullary bundles. , 



Fig. 235.— Mirabilis Jalapa. Transverse section through the young first epicotyledonaty internode (40). nt median 

 bundles^* united bundles of the leaf-traces passing through the internodfe> between m and v on either side are two 

 lateral bundles ; c extrafascicular cambium; the extensions of this protruding inwards are initial secondary bundles ; two 

 of the latter are separated from the cambium by a layer of parenchyma (left white). 



The first one or two of these bundles, which are outside the leaf-traces, always became 

 visible as young initial bundles at the same time as the cambium, but were separated 

 from it by a narrow zone of parenchyma : it can hardly be doubted that they, like those 

 which are subsequently formed, are really derived from the cambium. As soon as the 

 ring of cambium is clearly seen, successive new initial bundles are formed in it, which 



