458 • SECONDARY CHANGES. 



the bundles of the trace. The descriptions which follow below will explain this 

 in greater detail. The formation and orientation of the cambial zone are once more 

 the same as in other cases. Hartig^ and Sanio state that this condition exists in 

 the case of Ephedra monostachya, Cheiranthus Cheiri, and Miihlenbeckia complexa, 

 Hieracium, Pyrethrum, Galium, Plantaginese, and other plants to be mentioned imme- 

 diately. I find it in Cobaea, Crassulaceae " (Sedum spec, Sempervivum arboreum, 

 Echeveria pubescens), Caryophyllese ^ (Dianthus plumarius, Silene italica), Rumex 

 lunaria. Campanula Vidalii, Lobelia syphilitica, Xanthosia rotundifolia, and Centradenia 

 grandifolia. INIany other Melastomaceae, and, according to Chatin's ^ description, the • 

 Rhinanthaceoe also, appear to behave in the same way, but here it is not admissible 

 to draw any certain conclusion from one or the other species, as to the behaviour even 

 of its nearest allies ; thus, for example, Rumex alismifolius, in contradistinction to the 

 R. lunaria just mentioned, possesses the structure given under (d). Comp. also below, 

 Sect. 147. 



Sect. 135. According to the traditional terminology, the part of the ring lying 

 on the inside of the cambial zone, and including in itself the whole of the xylem 

 groups, is called, in stems of the Dicotyledonous type, the zvood or /igneous body 

 {xyletn of Nageli), while everything that lies outside the cambial zone is called the 

 cortex. The latter is divided into the basl zone, bast or liber* (phloem) which, 

 limited internally by the Cambium, includes and is characterised by all the phloem- 

 groups of the ring, and the external cortex ^, Duhamel's Enveloppe cellulaire, lying 

 outside this. _, In the ligneous body the elements of the vascular bundles form strands 

 with the arrangement described, wood-strands ; the bast has similar bast-strands, cor- 

 responding in their arrangement to the wood-strands; or, if one will, the two may 

 be termed xylem and phloem strands. The bands of non-equivalent tissue — consisting 

 in the great majority of cases of parenchyma — lying between the strands, and having a 

 radial course, as seen in cross-section, are called medullary rays. Each of the latter 

 consists of a portion belonging to the ligneous body, the medullary-ray of the wood 

 (' Markstrahl katexochen ' of Nageli), and of a portion lying in the bast-zone 

 (cortical medullary-ray, cortical ray of Nageli). Those medullary rays which are 

 formed on the first origin of the woody ring pass through from the pith to the 

 external cortex. They have accordingly been termed large medullary rays, in con- 

 tradistinction to those which arise later, and do not reach the pith, and are thus in 

 this respect smaller rays. With reference to their origin at the first commencement 

 of the woody ring, the former have also received the name of the original, primary 

 rays. 



The genetic relations which are indicated by the latter term are not, however, 

 the same in all cases for the anatomically similar large medullary rays, as follows 

 from what has been stated above. In the case described under (i) they are identical 

 with the original rays, and thus the expression primary medullary rays is appro- 



' Botan. Zeitg. 1859, P- 94- 



"^ Regnault, Ann. Sci. Nat. 4 ser. torn. XIV. p. 87. — Hartig, I.e. 

 ^ Anat. Compar^e, p. 221. 



* ' Liber, seu interior corticis amictus, ligno contiguus, fibris reticulatis .... compositus.' 

 Malpighi, Anat. Plant, cap. I. 

 ^ Compare above, p. 236. 



