FIELD CROPS. 



131 



peroxidase, but except in a few cases it was found tliat peroxidase develops in 

 the seeds only when they are 20 years old or less. 



Studies on variegation and some accompanying' phenomena, H. Lindemuth 

 (Laadw. Jahrb., 36 {1901}, No. 5-6, pp. S07-S62, pis. 2, figs. 16).— A report is 

 given of studies made on variegation in a large number of plants, principally 

 species of Malvaceae. Various theories of variegation are discussed and the 

 results of extended experiments in the transmission of that phenomenon through 

 grafting, cuttings, and seedlings are given. 



Recent: investigations in plant breeding, C. Fruwikth (Jour. LandiD., 56 

 {I90S), No. 1, pp. S9-99). — Brief summaries are given of some recent contribu- 

 tions to the literature of plant breeding. Most of the investigations reiiorted 

 were carried on in Germany, France, Austria. FiUgland, and Italy. 



Ileports of the plant culture stations in Denmark, 1905-6 and 1906-7 

 ((■^epa rates from K. Dattske Landhiisli. ,sV7.s7,-. Aarshcr.. l90.',-(). pp. 51-112; 

 1906-1, pp. 55-160). — The reports cdutain suiinnaries of trials conducted at 

 various Danish State plant culture stations and accounts of other activities of 

 I lie stations during the years given. 



FIELD CROPS. 



Thirty years of crop rotations on the common prairie soil of Illinois, C. G. 

 Hopkins, .J. E. Readhimicr, and W. (t. Eckuardt {Illinois Sta. Bui. 125, pp. 

 323-356, figs. 8). — This bulletin reports the results of rotation experiments in 

 l)rogress for 13 and 29 years under different systems of farming. The original 

 experiment is described in a previous bulletin (E. S. R., 2, p. 559). 



The average corn yields of the last 3 corn crops grown in different cropping 

 systems in both series of experiments are given in the following table: 



Average corn yields for the last 3 crops loith different crop rotations. 



Crop years. 



Crop systems. 



Average yield per 

 acre. 



13-year 

 experi- 

 ments. 



29-year 

 experi- 

 ments. 



1905, 1906, 1907 

 1903, 1905, 1907 

 1901,1904,1907 



Bxi. 



Corn every year . 

 Corn and oats . . . 

 Corn, oats, clover 



liu. 



It was found that in 12 years of growing corn every year the yield became 

 I'educed from more than 70 bu. to 35 bu. per acre, and that during the next 16 

 years the decrease amounted to only 8 bu. During the first 11 years of the rota- 

 tion of corn and oats the yield decreased from more than 70 bu. to 62 bu., and 

 during the next 16 years a further reduction of 16 bu. occurred. In the 8-year 

 rotation, during the first ten years the yield decreased from more than 70 bu. to 

 66 bu., and during the next 16 years to 58 bu., the average reduction being only 

 ^ bu. per year. 



In a system of grain farming a 3-year I'otation of corn, oats, and clover was 

 followed. The cornstalks were disked down and in harvesting the oats as much 

 straw as possible was left in the stubble. The third year the clover was mowed 

 once or twice and left lying on the land. If the clover seed crop was successful 

 it was harvested and the clover straw returned to the soil. In addition, catch 

 crops of annual leguminous plants such as cowpeas were grown between the 

 corn rows. Special treatment was given some of the plats by applying lime at 



