Vil 
zones round the axis: these zones are intersected transversely by medullary rays 
radiating from the central pith. Occasionally, as above hinted, increase of 
thickness does not take place by means of annual Zones, the wood at whatever 
age appearing to consist of a single homogeneous zone. Dr. Lindley has taken 
advantage of this circumstance and brought together most of the families in which 
it occurs to form his group of Homegens distinguished by the Endogenous strue- 
ture of their wood. Descending still lower in the scale we come to two groups 
of cellular plants, the Rhyzanths mushroom like plants, and the Podostemons, 
sea-weed like plants, agreeing with alge in almost every thing except their 
fructification. 
The leaves of Dicotyledons are, usually attached to, and separate from the 
stem by an articulation and are reticulated, that is their veins anastomose and form 
a net work, but this is not quite absolute as it is wanting in the leaves of most of 
the Gymnosperms. 
The flowers are for the most part quinary in the number of their parts and - 
are generally furnished with both calyx and corolla; but departures from both 
these rules are frequent: most of the Homogens have ternary, and many fami- 
lies quaternary flowers, while numbers have no corolla. 
The seed is usually enclosed in a pericarp, but here also a striking ex- 
Ception occurs, the whole of the coniferus family, forming Lindley’s Gymnosperms 
having naked ovules and seed, a privation combined with some interesting peculi- 
arities of the Anatomical structure of the whole plant. The seed itself is either per- 
fect or imperfect, that is, is furnished with an Embryo having two or more op- 
posite cotyledons, or is sporulose : imperfectly developed as in Rhyzanths. ‘The 
Embryo also is perfect or imperfect, with or without albumen. ‘The albumenous 
ones are intra or extra albumenous, enclosed within the albumen like the -yoke 
within the white of an egg, or placed on the outside of it, as in the case of the 
curvembryate orders. 
From this description, brief and imperfect as it is, we find there are five mo- 
difications of structure, as regards vegetation, forming so many distinct groups. Ist 
Exogens as generally understood with the wood in Zones: or concentric circles : 
2d Homogens, first associated as a distinct group by Dr. Lindley: 3d Gymnogens 
or conifere: 4th Rhyzanths having more the structure of Fungi than perfect plants 
and Sth Podostemons which seem to have an anatomical structure nearly allied 
to alge, but which Mr Griffith has determined, from actual dissection of the seed, 
to be dicotyledonous. Then as regards the structure of the seed, there are exal- 
bumenous and two modifications of albumenous Embryos ; and a fourth where it 
is imperfect. The albumen, moreover, greatly varies in quantity, being sometimes 
yery abundant with a minute Embryo, varying thence to a large embryo and very 
sparing albumen. 
