SOIL EXHAUSTION AND ROTATION OF CROPS. 201 



lowed to go to seed. I have myself observed that where Timothy 

 seed was raised the crop of grass the next year was very small, 

 although the soil was excellent. The plants had Buffered severely 

 from being allowed to go to seed, notwithstanding Timothy has a 

 bulb at the root, which should fortify it considerably against tins 

 strain, and a small seed, which renders the exhaustion less than is 

 the case with our bread grains. The production of seed is thus a 

 critical thing fur the life of the plant. 



Let us Consider again for a moment, the mode of growth of our 

 cereal grains. Sown in the spring, the plant comes up and grows, 

 slowly at first but with increasing vigor, up to the time of " head- 

 ing out" — a period of two months. Then the growth acquires its 

 greatest intensity. It heads out, blossoms, and the seeds begin 

 to form and ripen, and this whole process of seed production re- 

 quires but about a month when the weather is favorable for its 

 completion. 



In actual trials with the oat plant, it has been found by Bret- 

 schneider and Arendt that a large share of the growth of the over- 

 ground part of the plant occurs at the time of heading and blossom. 

 Thus the former observed that out of 6,886 lbs. of the dry acreage 

 yield of the oat, 3,099 lbs., or three-sevenths of the crop, were 

 produced from June 19th to July 8th, i. e., in nineteen days; the 

 total period of growth being one hundred and six days. Arendt 

 found that three-eighths of the total dry produce of the oat grew 

 in twelve days, 18th to 30th of June, the period of heading and 

 bloom, and during the twenty -two days between June 18th and 

 July 10th, nearly three-fifths of the growth took place. [LTow 

 Crops Grow, p. 205, et seq.] 



Before the seed is ripe the lower leaves begin to turn yellow, 

 and show "that their activity is diminishing or has ceased 

 altogether; and the ripening of the plant takes place to a great 

 extent, by the removal of matters which have been previously 

 stored up in the stem, leaves and roots, into the seed. You may 

 cut any of the grains at the root when the kernel is in the milk, 

 and the seed will still ripen, and although, if you cut it too early, 

 the kernel will shrink, it will be perfect in its parts and service- 

 able as seed grain. 



It thus appears that the cereal plant grows from the soil and 

 atmosphere until the seed arrives at a certain stage of develop- 

 ment, then the activity of the roots and foliage decreases, the 

 acquisition of food from external sources gradually diminishes, 



