404- H. von Mohl on the Cambium-layer 



into vascular bundles. But they are decidedly new structures, 

 and not prolongations or ramifications of the vascular bundles 

 of the stem . 



The branches of the roots of the Monocotyledons stand in the 

 same relation to the roots as the latter do to the stem, since they 

 are developed outside a cambium-cylinder which has ceased to 

 develo])e, and their ramifications penetrate backwards between the 

 vascular bundles of the root. Schacht (p. 101) denies that the 

 roots of Monocotyledons produce new branches, if their cambium- 

 cylinder is lignified early ; but this is untrue, and he should 

 have paid attention to what has been said on this subject by 

 Karsten (p. 56), who was supported by totally difi"erent experi- 

 ence. The origin of the thick adventitious roots of Pandanus 

 presents conditions analogous to that of the Palms ; and Schacht 

 (p. 320) is wrong in ascribing to their stems a continuously 

 developed cambium -layer such as occurs in Dracana. 



Less evident, and, particularly in the Dicotyledons, less con- 

 vincing on account of the presence of an active cambium-layer 

 in which the adventitious roots originate, is the condition of the 

 roots of herbaceous Monocotyledons and the radical branches 

 and adventitious roots of the Dicotyledons, in which the earliest 

 vessels belonging to the root appear in the form of a wreath of 

 vessels, and lie upon the lateral surfaces of the subjacent vascular 

 bundles ; but Trecul* was right in regarding the circumstance 

 that these vessels are not continuous with the vessels of the 

 stem or of the roots from which the new roots arise, as a proof 

 that the adventitious roots possess vessels of their own. 



With regard to adventitious buds, also, it may be proved that 

 they form their own system of vascular bundles. The evidence 

 is indeed not striking in the common cases where the adven- 

 titious buds form in the cambium-layer of the Dicotyledons, on 

 which account I shall not dwell uj)on this subject, so well inves- 

 tigated by Trecul (/. c. p. 268). Perfect proof can only be 

 afforded by those adventitious buds which originate in fully- 

 developed cellular tissue at a distance from the cambium-layer 

 of the })arent plant, in which case there can be no doubt of the 

 origin of their vascular bundles. Trecul (p. 280) observed one 

 case of this in fragments of the roots of Ailanthus, in which 

 adventitious roots had been formed outside the liber-layer : these 

 stood in connexion with the cambium-layer of the stem by means 

 of vessels which appeared to be younger than those contained in 

 the bud. We cannot indeed attribute perfect conclusiveness to 

 this observation, since it did not include the earlier stages of 

 development, and only shows the probability, but not the cer- 

 tainty, of the independent development of the vascular bundles 

 * Ann. lies Sc Nat. 'A ser. viii. p. 2!>(). 



