36 PLANTING BUiBS AND TUBERS, 
air nas been doing for them: but young plants, when they hinvete 
panded two or three pairs of leaves, and when the stock of carbon 
contained in their cotyledons, or in their seeds, is exhausted, require 
light to enable them to elaborate their sap, without which the pro- 
cess of vegetation could not go on. Abundance of light also is fa- 
vourable to the development of flowers and the ripening of seeds; as 
it aids the concentration of carbon, which they require to make them 
fertile. The curious fact that seeds, though abundantly supplied 
with warmth and moisture, will not vegetate without the assistance 
of the air, was lately verified in Italy; where the Po, having over- 
flowed its banks near Mantua, deposited a great quantity of mud on 
some meadows; and from this mud sprang up a plentiful crop of 
black poplars, no doubt from seeds that had fallen into the river from 
arow of trees of that kind, which had formerly grown on its banks, 
but which had been cut down many years previously. Another in- 
stance occurred in the case of some raspberry seeds found in the 
body of an ancient Briton discovered in a tumulus in Dorsetshire. 
Some of these seeds were sown in the London Horticultural Socie- 
ty’s Garden at Turnham Green, where they vegetated, and the plants 
produced from them are still (1840) growing. Numerous other 
nearly similar instances will be found in Hooker’s Botanical Mis- 
cellany, Lindley’s Theory of Horticulture, Jesse’s Gleanings, and nu- 
merous other works. Steeping seeds in oxalic acid, &c. to make 
them vegetate, is efficacious; as there is a speedier combination 
between the carbon in the seeds, and the oxygen in the acid, than 
can be effected by the ordinary agency of the air in parting with its 
oxygen to them. a 
Planting bulbs and tubers bears considerable analogy to sowing 
seeds. ‘The -ulb or tuber may indeed be considered as only a seed 
of larger growth, since it requires the combined influence of air, 
warmth, and moisture to make it vegetate, and then it throws out a 
stem, leaves, and roots like a seed. There is, however, one impor- 
tant difference between them; the seed expends its accumulated 
stock of carbon in giving hirth to the root, stem, and leaves, after 
which it withers away and disappears ; while the bulb or tuber con- 
tinues to exist during the whole life of the plant, and appears to con-’ 
tain a reservoir of carbon, which it only parts with slowly, and as 
circumstances may require. Though bulbs and tubers have here 
_ been mentioned as almost synonymous, modern botanists make sev- 
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