DEVELOPMENT. 638 
life, the history of which will here be briefly 
traced from that period of its early growth at 
which the plumule of the embryo, after just 
emerging from its seed cover, has reached the 
surface of the ground, and has there unfolded 
its twin incipient leaves. The cells of the cell 
system of which, as we have explained, the em- 
bryo plant is formed, are at first very minute, 
consistently with the wise and beautiful eco- 
nomy of space observed throughout the natural 
world. Hverything, indeed, in the delicate struc- 
ture of the incipient plant is moulded on the 
smallest possible scale, for the reason that the 
means of necessary growth are provided in the 
elemental substances existing in the earth. The 
walls of the early cells are very thin, and the cell 
cavities are full of the protoplasmic matter which 
is—if the expression may be used—the life-blood 
of the plant. In the centre of each cellular mass 
of protoplasmic fluid, surrounded by its investing 
walls of cellulose, there may be observed a rounded 
substance darker than the general mass—the 
word ‘mass’ is used as a convenient expression, 
although it will be understood that it refers to 
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