CONDITIONS OF GROWTH. 465 



for at least 2000 years, and which are drawn from an examination of the 

 aerial contents of vessels said to have been obtained from Pompeii or 

 Herculaneum, are of very little account. We have only to recollect how 

 easily diffusion takes place through crevices, and even almost invisible 

 pores. But there are proofs of a far higher order, and of a much more 

 general kind, which might be brought forward, if this were the proper 

 place, establishing beyond all possibility of contradiction the fact that in 

 a slow manner, through countless ages, the constitution of the atmosphere 

 has changed, and that now, through the operation of conditions which 

 have spontaneously arisen, it has come into a condition of apparent 

 equilibrium. 



When, therefore, a seed is placed in the ground in the warm season of 

 the year, the germ it contains develops, and, after a few days, makes its 

 appearance as a young plant at the surface. If the growing structure is 

 examined during its passage through the soil, it presents a pale yellow- 

 ish aspect, which is exchanged for a bright green tint as soon as it 

 escapes from its confinement, and unfolds itself to the sunlight and the air. 



From the first moment, until the green color is assumed, the young 

 plant is nourished, as we have seen, at the expense of the Infantile and 

 seed. In anticipation of this, the parent had laid up a stock adult life of 

 of nutritive material. On this the embryo draws, consuming P lant f- 

 a part in the support of its life, and incorporating the residue in its 

 structure ; but as soon as the surface of the soil is gained, this life of de- 

 pendence ends ; the plant weans itself, and, abandoning its temporary 

 support, commences to collect from the air and the earth tfie materials of 

 which it is to consist. Its infantile seed-life has closed ; its independ- 

 ent aerial life has begun. 



In this aerial life, which is the mode of existence destined to continue 

 until absolute death occurs, the two essential conditions to g umma O f 

 which we have drawn attention are recognized. There must the conditions 

 be a steady supply of material for the building up of the grox 

 growing structures, and this has to be derived from external sources. 

 There must also be a capability of so grouping or moulding the material 

 thus acquired that the various parts that are wanted leaves or fruits, 

 flowers or thorns, may be made. 



The manner in which these conditions are satisfied presents to a re- 

 flecting mind one of the most wonderful examples of the system of na- 

 ture. We have already shown that the power of moulding and group- 

 ing is inherent in the plant. In virtue of this, while it was yet in the 

 ground, and therefore in the dark, the germ could put up its stem and 

 fashion its imperfect leaves, but it did not possess any power to gather 

 nourishment beyond that which was stored up in the seed, and had that 

 stock been exhausted before it reached the surface, it must have died. 



GG 



