As annual plant starting from the seed,forms first a small root and then a small shoot.utilizing for the purpose the food stored in the seed.and proceeds togrow in both directions till it flowers,sets seed and diees. During the life-history it nourishes itself from two sources from the soil by means of its roots, and from the air by means of its green parts. The nutritive substances obtained from these two sources are of two very diffeerent kinds.but both are necessary for growth.The roots take in water mineral saits, among which the ost important salts from our present point of view are nitrates,which are built up inside the plant into more complex nitrigeneous substance, whilst the leavs.such as sugar or starch.
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