_Straw_ is almost universally used for this purpose. Besides being one of the bye-products of the farm, it is admirably suited in many ways, both owing to its peculiar shape--its tubular structure being excellently adapted for this purpose--as well as on account of its composition, being largely composed of cellulose, a very absorptive substance. Straw thus possesses considerable absorptive power. In manurial ingredients it is not very rich; for, of the various parts of the ripened plant, straw contains the least percentage of nitrogen and phosphates. This is due to the fact that, as the straw ripens, a considerable proportion of these ingredients passes up from the stalk to the seeds, where they are retained. Generally speaking, straw may be said to contain not more than _a half per cent_ of nitrogen--_i.e._, 11.2 lb. per ton. Its percentage of nitrogen varies, of course; the recorded analyses[143] for wheat-straw ranging from .22 to .81 per cent, or furnishing an average of .48 per cent--_i.e._, 10.75 lb. per ton. Barley-straw is somewhat richer in nitrogen, the recorded analyses ranging from .41 to .85 per cent, or giving an average of .57 per cent--_i.e._, 12.76 lb. per ton; while oat-straw is the richest of the commoner straws, ranging from .32 to 1.12 per cent, an average of .72 per cent--_i.e._, 16.12 lb per ton. Of mineral matter, however, straw contains a very much larger percentage, proportionally, than of nitrogen; for, with the exception of phosphates, there is a considerable quantity of inorganic fertilising matter, in the shape of potash, lime, &c., present in Composition of Straw.[144] -----------------+---------------+------------------------+-------- | Ash. | Composition of Ash. | +------+--------+------------------------+ | | | Lb. per ton. | | | Lb. |-------+----------+-----| Number | Per | per |Potash.|Phosphoric|Lime.| of | cent.| ton. | | Acid | |Analyses -----------------+------+--------+-------+----------+-----+-------- Wheat (winter) | 5.54 | 124.09 | 18.61 | 5.05 | 7.18| 8 Wheat (summer) | 5.14 | 115.13 | 25.76 | 6.47 | 7.12| 6 Rye (winter) | 5.33 | 119.39 | 20.61 | 5.89 | 9.73| 8 Rye (summer) | 6.14 | 137.53 | 42.41 | 6.73 |10.53| 1 Barley | 4.90 | 109.76 | 26.83 | 5.75 | 8.73| 8 Oats | 5.09 | 114.01 | 26.22 | 4.17 | 9.12| 4 -----------------+------+--------+-------+----------+-----+--------