FLESHY ROOTS 697 



character. Such fleshy roots exhibit various anomalies in their 

 secondary growth, all of which tend in the first place to ensure the 

 development of a suitable parenchymatous storage-tissue ; in addition, 

 the anomalous cambial activity often leads to the multiplication and 

 appropriate arrangement of the conducting strands required for the 

 deposition and removal of the reserve- materials. 



The morphological value of the parenchymatous storage-tissue 

 varies greatly in different fleshy roots. In many cases there is a 

 massive development of extra-cambial storage parenchyma, corresponding 

 either to primary cortex (lateral roots of Asclepiadaceae and Piper- 

 aceae) or to secondary phloem (Taraxacum, Ruhia, Umbelliferae). 

 In either instance the secondary growth cannot strictly be termed 

 anomalous, the deviation from the normal conditiou consisting solely 

 in the relatively feeble development of the woody cylinder, as com- 

 pared with the extra-cambial tissues. In another series of types the 

 storage-tissue owes its origin to the massive development of the paren- 

 chymatous elements of the wood that is, of the xylem-rays or xylem- 

 parenchyma ( Urtica, Cucurbita, Symphytum officinale) ; the latter 

 condition is excellently illustrated by the napiform roots of Brassica 

 and Raphanus, where the secondary xylem consists of a massive paren- 

 chymatous tissue, which is traversed by strands of vessels accompanied 

 by a certain number of fibres. These fibro-vascular strands the term 

 is highly appropriate in the present case are arranged in regular 

 concentric circles, and form a network with vertically elongated 

 meshes. In roots of this type, the anomaly consists essentially in 

 the aberrant composition of the xylem ; the characteristic peculiarity 

 of the wood is often accentuated by the fact, that the distinction 

 between xylem-parenchyma and medullary ray tissue is not strictly 

 maintained (Scorzonera hispanica, Raphanus, Brassica). 



J. E. Weiss has shown, that in a number of fleshy roots, tertiary 

 vascular bundles may be differentiated within the storage parenchyma 

 of the secondary xylem; in Oenothera biennis these tertiary strands 

 consist solely of leptome, whereas in C'och/earia Armoracia, Brassica 

 Napus, B. Rapa, Raphanus sativus, and Gentiana lutea they take the 

 form of concentric bundles with central leptome. In Bryonia dioiea 

 the adventitious cambium surrounds the vascular strands of the woody 

 cylinder, forming additional vessels in immediate contact with the pre- 

 existing ones, and cutting off leptome tissue on its outer side. 



The secondary growth in thickness exhibits even more striking 

 anomalies in those roots which develop several cambial layers in 

 succession. In the Beet-root (Beta vulgaris), a second cambium arises 

 by tangential division in the parenchyma situated outside the primary 

 cambial zone ; it is only active for a limited period, and is in its turn 



