i37 
of the terms ‘ Phyllome 9 and ‘ Caitlomei 
arrangement is characteristic of the stem, to the upper ex- 
panded portion where the structure of tissues and orientation 
of bundles is throughout characteristically foliar, the bundles 
first separate into groups, each group having as its centre a 
relatively large bundle, which is so placed that the xylem is 
directed towards that surface (the morphologically lower) 
which is ultimately directed upwards, and the smaller 
irregularly arranged bundles then coalesce with the larger 
one. Thus we have here the converse case of a member, 
which on other grounds would be recognised as an axis, 
showing in its lower portion an axial type of internal 
structure, which gradually changes in its upper portion to 
that laid down by Van Tieghem as characteristically foliar. 
Though other examples might be adduced, these will suffice 
to show that morphological distinctions of the parts of the 
shoot cannot be based on the disposition or orientation of 
the vascular bundles : equally insecure would be conclusions 
based upon their number, as is obvious when it is remembered 
that scale-leaves are often without vascular bundles at all, and 
that the cotyledon of Lycopodium may show a similar sim- 
plicity of structure 1 ; also the case of the genus Gnetum may 
be cited, in which I have already shown 2 3 that in one species 
( G . africanum) the central bundle, which is present in other 
species, is absent, though there is no corresponding difference 
of configuration. And lastly, observations on the point of 
fusion of vascular bundles from one member with those of 
another give only uncertain ground for morphological con- 
clusions, since we know that in cases where there is no question 
of morphological character the fusions may take place at very 
irregular points (e.g. the shoot of Helianthus). 
From the examples above quoted (and they might be 
greatly added to) it appears that observations of the arrange- 
ment, orientation, number, or point of fusion of vascular 
bundles constitute an insufficient foundation for the solution 
1 Treub, Ann. Jard. Bot. Buit. vol. iv. p. 134, in Z. cernuum. Goebel, in 
Bot. Zeit., 1887, in Z. inundatum. 
3 Phil. Trans., 1884, Part ii. p. 599. 
L 
