1 35 
of the terms ‘ Phyllome ’ and ‘ Caulome! 
wrote, with special reference to the leaf 1 , as follows : ‘ We shall 
show that in the whole series of vascular plants all the bundles 
of the leaf are in their disposition and orientation placed with 
reference to a plane which includes the axis of symmetry of the 
stem and the radius of insertion ; 5 and continues, ‘thus while the 
plant-axis in both parts, viz., root and stem, which compose 
it, is throughout symmetrical with reference to a line, the 
appendage is only symmetrical with reference to a plane . 5 
This method of distinction, which its author applied to the 
solution of various morphological problems in connection with 
the flower, was taken up and further elaborated, and still 
more precisely stated by Bertrand 2 ; and if the constancy of 
structure of corresponding members of all vascular plants 
were greater than it is, the anatomical method might doubt- 
less prove a ready and efficient rule of thumb for distinguish- 
ing different categories of members and solving morphological 
problems. Unfortunately numerous known facts are against 
this : it will be well to cite a few pregnant exceptions to the 
rules as above laid down, and these are to be found especially 
in shoots of peculiar conformation. 
In various species of Juncus a foliage leaf projects beyond 
the apparently lateral inflorescence as an elongated conical 
or nearly cylindrical structure, which shows just above the 
inflorescence a sheathing base ; if transverse sections of this, 
which is actually a leaf, be examined, those cut through the 
sheathing portion show an arrangement of the tissues which 
would fall under Van Tieghem’s definition of a leaf ; but in the 
1 We need not here refer to the anatomical distinction of stem and root, since 
we are at present specially concerned with the leaf. It is, however, to be noted 
that Van Tieghem began his researches on. the root, which is much less subject to 
metamorphosis than stem or leaf, and it might accordingly be expected that its 
type of structure would be more uniform than theirs ; he found but few roots of 
aberrant structure. His researches on the stem and leaf have, I believe, never 
been completed, and in his Traite de Botanique he lays no great stress upon the 
anatomical method of distinction of parts of the shoot. It may perhaps be con- 
cluded from this that he has not found the anatomical method apply so readily to 
the more plastic members of the shoot as it does to the more uniformly constructed 
root-system. 
2 Archives Botaniques du Nord de la France, 1881. 
