20 
THE FOOD OF TREES IS IMBIBED [Part II. 
The unripe 
ends of roots 
not imbibe. 
Formation of 
ends of roots. 
In the first growth of the seed, in the growth 
of cuttings and of coiled branches, and in the 
growth of the half-radishes, there must be ab¬ 
sorption from the surface without the aid of the 
small fibres or ends of roots, since no roots of 
any sort exist in any of these cases. 
Let us now consider the negative assertion, 
that plants do not imbibe by the unripe ends of 
their roots. 
Take the end of a freely-growing root; break 
or nip the silver end across. An internal tube 
will be found, distinct from the external tube. 
The difference in the organisation of the internal 
tube from that of the outer one will be plainly 
seen by the naked eye, and very frequently a 
circle of cells or tubes round the outside of the 
inner main tube. These two main tubes are 
what an Englishman would like to call the outer 
and inner bark: but he must not think of doing 
so ; he must call the outer tube the cuticle or 
epidermis, and the inner tube the parenchyma¬ 
tous under-layer or herbaceous envelope. Or, at 
least, they are equivalents to what would bear 
these euphonious titles above ground. Continue 
to break off small pieces of the root. A third tube 
will be found, — a ligneous thread, ending in the 
finest point, and growing gradually thicker. The 
