Development of Roots of Agricultural Plants^ 421 
If we look at the condition in which food is taken up by the 
absorbents, at least in the greater portion of the animal kingdom, 
it is at once apparent that in one respect the analogy fails. 
Whatever choice the spongelets may exercise in the absorption 
of nutritious matter ; whatever be the connection of the soil with 
the fluid holding plant-food in solution ; and whatever the possi- 
bility of minute, and especially nascent, particles not in solution 
being taken up ; elaboration is an after process. 
The roots of plants may conveniently be considered in three 
distinct stages of growth, viz., in their primar}- development, 
their stage of ramification, and their enlargement or differentiation 
as receptacles of nutriment for future exigencies. 
We have then to consider first, the very earliest stage of their 
existence, while still within the seed, or only just bursting through 
the envelopes. It is remarkable, that in phaenogamous plants the 
root-end of the embryo is always in the first instance turned to 
the little aperture or micropvle through which the pollen tube 
enters and comes in contact with the embryo-sac, and so effects 
impregnation, though as the ovule grows it often takes a different 
direction. In those cryptogams, as ferns and club-mosses, which 
come the nearest to phaenogams, exactly the contrary position of 
the embryo is maintained. This fact seems to indicate that even, 
in this very earlv stage of growth, the radicular extremitv has 
some important function above that of the cotyledons. 
The embrvo, consisting of one o" more cotyledons, the sponge- 
let, and the intermediate portion between that and the plumule, 
composed of the neck and true radicle, is either quite free within 
the coats of the seed, or is surrounded by a greater or less quantity 
of tissue, known by the general name of albumen, though the 
word does not bear the same import as it does in chemistry. This 
mass abounds in starch, and often in oil globules or other matters 
more or less easily convertible, while the coats are sometimes rich 
in gluten or other important substances. The spongelet, v. hich is 
the active part of the radicle?, consists of a mass of naked cells, 
more or less intimately connected with each other, and with 
more or less definite intercellular passages, which have, however, 
no communication with each other except through the walls of 
the adjacent cells. 
Since the time of Richard, botanists have divided phaenogams 
into two principal groups, endorhizal and exorhizal ; or those 
whose primary root is internal, and on germination bursts through 
the surrounding tissue, and those whose absorbent surface is abso- 
lutely naked. I have, however, long been of opinion that this 
distinction is not tenable, and depends more upon the peculiar 
structure of the embryo in cereals, than upon that of mono- 
