640 CHEMICAL PROCESSES IN THE PLANT. 



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 are 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 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 

 and medullary rays, where (as well as in the chlorophyll) it is always accompanied 

 by sugar ; and it is evidently this latter substance which brings about the diffusion from 

 cell to cell, and at the same time furnishes the material for the formation of new 

 starch-grains. The sugar is the migratory product which takes part in the diffusion ; 

 the starch-grains are the stationary transitional product. 



The distribution of starch and sugar shows moreover that they move from the 

 primary stem through the rachis of the inflorescence and the pedicels into the paren- 

 chymatous tissues, and penetrate into the young tissue of the flower, the growing fruit, 

 and the ovules, there to be employed in the production of cellulose. The distributed 

 starch collects more abundantly especially in the immediate neighbourhood of those 

 layers of cells which afterwards form the hard endocarp and the solid testa of the seed, 

 in consequence of its being required here in greater quantity, disappearing also from 

 them after the complete development of these layers of tissue. 



The sugar and starch are conveyed through the funiculus to the ovules ; they are 

 distributed through the integuments and the parts surrounding the nucleus ; and a large 

 quantity of sugar enters the growing endosperm, which supplies the material for the 

 formation of the oil which gradually accumulates, while fresh supplies of sugar are 

 constantly entering from without. In the growing embryo the cells are filled at a 

 certain period with fine-grained starch, which then entirely disappears and is replaced 

 by oil. All this indicates that the oil of the ripe seed of Ricinus is produced from the 

 starch and sugar which were transported to it from the assimilating organs during the 

 period of repose ; and even the hard woody pericarp and the testa obtain their formative 

 material from those substances. The albuminoids which collect also in the young leaves 

 and from which the chlorophyll-grains are formed, as well as that portion of these 

 substances which accumulates in the seed as reserve food-material, are transported from 

 the stem by the sieve-tubes and the cambiform cells of the fibro-vascular bundles. 



' In the Leguminosae^ a very important part in the transport of the reserve 

 proteinaceous substances is played by Asparagin. To demonstrate this, moderately 

 thin sections are placed in alcohol, and the saturation assisted by shaking. This mode 



* What follows is taken from a letter from Dr. Pfeffer. (Compare Book I, Sect. 8, p. 51). 



