ASSIMILATION AND METASTASIS. 
717 
only in the parenchyma of the leaf- veins ; the parenchyma of the hypocotyledonary 
portion of the stem, which is at present growing the most rapidly, contains only 
comparatively little oil but much starch and sugar ; and a number of the cells of the 
epidermis and parenchyma are filled with tannin. The primary root has first of all 
completed its growth in length and thickness (after germination it begins afresh) ; in 
its lower part it contains neither starch nor sugar (the former is present in the root- 
cap) ; in its upper part from which the lateral roots spring and in the lateral roots 
themselves sugar is still present, which is conveyed into the growing apices of the 
latter. When the hypocotyledonary portion of the stem has subsequently become 
vertical and has temporarily ceased to grow, the oil, starch, and sugar have almost 
entirely disappeared from it, and in their place the cell-walls have become thick, and 
the vessels and first cells of the wood and bast are already thickened. After the stem 
of the young plant has become upright, the cotyledons expand and grow rapidly, and the 
remainder of the oil which they had taken up from the endosperm now also disap- 
pears from them together with the starch and sugar. The seedling has now entered 
on a state in which the non-nitrogenous reserve-materials are consumed ; a framework 
of large and solid cell-walls is produced in their place ; and a quantity of tannin remains 
behind in some of the cells as a secondary product, as well as various other substances 
not present in the seed. 
The albuminoids which form so peculiar and intimate a mixture with the oil in the 
ripe seed, and which are partially contained in the aleurone-grains of the endosperm in 
the form of crystalloids, are, during the processes which have been described, transferred 
to the embryo, where they produce the protoplasm. During the whole of the period 
of germination the cells of the fibro-vascular bundles are found to be densely filled with 
albuminous substances, subsequently only those of the phloem ; these substances are 
evidently in motion toward the apices of the roots where new cells are continually 
being formed. Every young rudiment of a lateral root behaves to reagents as an 
accumulation of albuminous substance on the side of the fibro-vascular bundles of the 
primary root. But a very considerable portion of this material remains in the upper 
part of the stem of the seedling where new leaves are formed, and a still larger portion 
in the cotyledons themselves, where it furnishes the material for the formation of the 
numerous chlorophyll-granules. 
After the consumption of the reserve-material at the end of the period of germi- 
nation, the cells — with the exception of the youngest parts of the buds and the apices 
of the roots — are destitute of any formative material; although it has grown to a 
large size and contains a great quantity of water, the dried weight of the plant is 
very small and even less than that of the seed, because a portion of the substance 
has been destroyed in the process of respiration. But active organs have been formed 
from the earlier inactive store of material ; the roots absorb water and dissolved food- 
material ; the green cotyledons begin to assimilate ; they produce starch in their chlo- 
rophyll ; and the same substance is subsequently found also in the parenchyma of the 
petioles and in the stem as far as the bud, the young leaves of which grow from the 
products of the assimilation of the chlorophyll. At first the unfolding of new leaves 
and the increase in length and thickness of the stem and roots are very slow ; but the 
capacity for work possessed by the plant increases with every freshly developed leaf and 
every new absorbing root ; on each successive day it can produce a larger quantity 
of formative material than on any preceding one, and thus the rate of growth also 
increases. 
If a Castor-oil plant is examined at the time when vegetation is most active, when 
the green leaves supply the material for metastasis in all the organs, starch is found 
in their chlorophyll-granules and distributes itself from them through the parenchyma 
of the veins and petioles downwards into the stem as far as the root, and upwards 
to the young leaves which are not yet in a condition to assimilate. The excess which 
is not immediately required for the purposes of growth becomes deposited in the pith 
