ORIGIN OF ENDOGENS FROM EXOGENS. 513 



stage reached, when the internodes are arrested, may, perhaps, 

 result from a simple dislocation of the cords, so that the regular 

 series of circles is broken up, and the ordinary type of an endo- 

 genous stem results. 



The Radiciferous Net. — Henfrey, who examined the rhizome of 

 Victoria regia, brought out a point of some importance: in that 

 lie noticed the fibrous plexus, which is now called the M radici- 

 ferous net/' so characteristic of many endogens, from which arise 

 the cords to supply the adventitious roots. While, however, 

 this net is distributed over the whole surface of the central 

 cylinder* in endogens, so that roots can arise anywhere, in 

 Victoria it is isolated at the bases of the leaves, so that roots 

 only arise at those places. Hence the presence of the localized 

 radiciferous nets shows another approximation to the endogenous 

 type. After describing the characteristic features of Endogens 

 and Exogens, Prof. Henfrey wrote : — " Applying these con- 

 siderations to the structure presented by the stem of Victoria, 

 y\e find unmistakable resemblance to the typical structure of 

 Monocotyledons in the arrangement of its bundles, and the 

 entire absence of that kind of regularity which produces an 

 annular appearance of the fibro-vascular structure in a cross 

 section; the great number and the isolation of the bundles, and 

 the absence of a central medullary region, are especially monoco- 

 tyledonous ; and the relative position of the bundles in their course 

 is closely in agreement. The chief difference consists in the 

 collection of the bundles together into a kind of cord, where 

 they run out from the central region into the petiole j — which 

 arises from the comparatively narrow base of the leaf at its 

 origin in the punctum vegetationis, — and in the existence of 

 numerous bundles connected with the roots running up and 

 down and around the stem in the region immediately within the 

 rind. The former of these points indicates an agreement wita the 

 Dicotyledonous type : the latter departs less from the Monoco- 

 tyledonous type than from the Dicotyledonous." 



In Nelumbium codophyllum M. Trecul noticed a complete zone 

 of vessels, their axes often horizontal, surrounding a medulla. 



"Origine et Insertion des Racines Adrentires," L. Man gin, Ann. des Sci. 

 Nat 6 ser. xiv. 1882, p. 1>16; of. pi. 11. figs. 21, 22. 



t "On the Anatomy of Victoria regit," part h., Phil. Tr^ns. 18fi0. p. 479. 



2p2 



