Special Morphology and Classification. | 357 
covered up by the cork-tissue. The cortex very commonly 
exhibits also crevices and furrcws on the outside, and is often 
partially thrown oft in the form of dark. The portions of the 
cortex which are fresh formed every year are collectively dis- 
tinguished as secondary cortex, in contradistinction to the layer 
of primary cortex already formed in the ‘ punctum vegeta- 
tionis.”. No new elements are formed in the primary cortex ; 
while the secondary consists of the bast-portion of the vas- 
cular bundles and of intermediate tissue. 
With the exception of a few abnormal cases, the fibro- 
vascular bundles cither lie, as in Monocotyledons, isolated in 
the fundamental tissue (Fig. 472 A), or constitute a. hollow 
cylinder traversed by narrower intermediate striations, the 
medullary rays (Fig. 95, u. p. 68). They are developed in 
the neighbourhood of the ‘punctum vegetationis,’ either 
out of isolated cambium-bundles, or out of separate parts 
of a closed cambium- or thickening-ring (Fig. 472, B; see — 
also p. 64). There is thus formed on the inner side of each 
vascular bundle a xy/em-fortion, on the outer side a das¢- or 
phloéim-portion, these two parts remaining separated from 
one another by the thin-walled formative tissue. The mode 
of the further development of the vascular bundles has not 
yet been fully determined ; because it is scarcely possible to 
observe the first formation of the cambium-bundle in the 
‘punctum vegetationis,’ or in seedlings, the investigation of 
which could alone give the clue. It is therefore not yet 
accurately known whether the leaves are penetrated by 
ramifications of the vascular bundles of the stem, or whether 
they form bundles of their own which unite with the cauline 
bundles (those of the stem). The latter view seems to be 
supported by the fact that in a large number of cases fully 
developed bundles arise first at the apex of the leaf, their 
further development advancing thence downwards towards 
the base. It is, nevertheless, not improbable, from the 
regularity of their growth, that this latter development: of 
the vascular bundles follows those cambium-strings which 
