It is ascertained, also, that the weight of hay or straw reaped, is actually less when allowed to become fully ripe; and therefore, by cutting soon after the plant has attained its greatest height, a larger quantity, as well as a better quality of hay, will be obtained, while the land also will be less exhausted. The same remarks apply to crops of corn,—both to the straw and to the grain they yield. The _rawer_ the crop is cut, the heavier and more nourishing the straw. Within three weeks of being fully ripe, the straw begins to diminish in weight, and the longer it remains uncut after that time, the lighter it becomes and the less nourishing. On the other hand, the ear which is sweet and milky a month before it is ripe, gradually consolidates, the sugar changing into starch, and the milk thickening into the gluten and the _albumen_[22] of the flour. As soon as this change is nearly completed, or about a fortnight before ripening, the grain contains the largest proportion of starch and gluten; if reaped at this time, the bushel will be heavier, and will yield the largest quantity of fine flour and the least bran. [22] _Albumen_ is the name given by chemists to the _white of the egg_. A small quantity of this substance is present in every kind of grain. It is closely related to gluten. At this period the grain has a thin skin, and hence the small quantity of bran. But if the crop be still left uncut, the next natural step in the ripening process is, to cover the grain with a better protection, a thicker skin. A portion of the starch of the grain is changed into woody fibre,—precisely as in the ripening of hay, of the soft shoots of the dog-rose, and of the roots of the common radish. By this change, therefore, the quantity of starch is lessened and the weight of husk increased; hence the diminished yield of flour, and the increased produce of bran. Theory and experience, therefore, indicate about a fortnight before full ripening as the most proper time for cutting corn. The skin is then thinner, the grain fuller, the bushel heavier, the yield of flour greater, the quantity of bran less; while, at the same time, the straw is heavier, and contains more soluble matter than when it is left uncut until it is considered to be fully ripe.[23] [23] On this subject the reader will consult with advantage an excellent practical paper in the _Quarterly Journal of Agriculture_ for June 1841, by Mr. Hannam of North Deighton, Yorkshire, to whom I have to express my obligations for information regarding the results of some further experiments made by him during the last autumn (1841). SECTION IV.—ON THE ABSOLUTE QUANTITY OF FOOD YIELDED BY DIFFERENT CROPS. The quantity of food capable of yielding nourishment to man, which can be grown from an acre of land of average quality, depends very much upon the kind of crop we raise.