226 EXPERIMENT STATION KECOED. [Vol.37 



cortical tissues just beneatli the epidermis on the ventral side and extending 

 around the cortex. There is neither indication of cell division in the tissue 

 involved nor evidence of alteration of cell walls by dissolution of the middle 

 lamellae or elongation and softening of the entire wall. The separation of the 

 cells appears to be due mainly to increased turgor. Contact may persist until 

 some mechanical agency, as a slight shaking or tapping, breaks the epidermis 

 and the few tracheal elements which may remain intact. The number of cells 

 actually concerned in the process of abscission is greater in the hybrids men- 

 tioned than in the parental species, and the same is true of automatic as con- 

 trasted with spontaneous abscission. 



FIELD CROPS. 



[Report of field crops work at the Minnesota Station] {Minnesota Sta. Rpt. 

 1916, pp. 38-42). — Additional data on the cost of tobacco growing are re- 

 ported. The estimated cost per acre was $36.53, as compared with $24.25 

 previously reported, due chiefly to adverse weather conditions necessitating 

 extra hand labor. The yield averaged 1,280.51 lbs. per acre, selling at an 

 average price of 7.5 cts. per pound, and graded as filler. 



Selection tests are reported with winter and spring wheat and with oats, as 

 well as cultural studies with alfalfa, Sudan grass, and sweet clover. 



The results of crop rotation experiments show increased yields of 13.7 per 

 cent for corn. 14.95 per cent for oats, and 30.98 per cent for wheat, secured in 

 a 4-year rotation of oats, wheat, clover, and corn, as compared with continuous 

 cropping. In the same rotation increases in net gains per acre, as compared 

 with continuous cropping, were for corn 21.4 per cent and for wheat 72.3 per 

 cent. 



Corn yields on land plowed in the fall and early spring were practically 

 equal. The growing of oats and the securing of a stand of clover and timothy 

 on spring-plowed land was not so satisfactory as on fall-plowed laud or on 

 double-disked corn land. 



[Report of field crops work at the Crookston substation] {Minnesota Sta., 

 Rpt. Crookston Substa., 1910-1916, pp. 27-70, 81, 82).— Cultural, variety, fer- 

 tilizer, and rotation tests are reported, together with brief notes on corn-breed- 

 ing work and methods of weed eradication. 



Rate-of -seeding tests have been conducted with corn, oats, barley, spring and 

 winter wheat, and winter rye. The winter cereals have not proved satisfactory, 

 owing to excessive winterkilling, while tests with spring-sown grain have failed 

 to give conclusive results and will be continued. 



Tests of different methods for protecting winter wheat were begun in 1911 

 but faHed to give very satisfactory results until 1916. Wheat sown on corn 

 left uncut yielded 43.5 bu. in 1912 and 32.1 bu. In 1916. Wheat sown on corn 

 stubble and covered with 1 ton of straw per acre yielded 28.8 bu. In 1910. The 

 tests with straw covering are to be continued. 



Trials of seeding alfalfa and red and sweet clover with wheat and oats at 

 different rates as nurse crops, and with no nurse crop, were begun in 1915. 

 With a nurse crop, in 1915, a stand of 60 per cent and low vigor resulted with- 

 out any apparent difference between the rates of seeding, while without a nurse 

 crop, a 100 per cent stand and excellent vigor were secured. The 1916 results 

 were rather contradictory, due to the relatively short and less rank growth of 

 the nurse crops. Field tests with alfalfa to determine the relative importance 

 of various factors in their influence upon tlie growth of the crop indicated that 

 they rank as follows : No nurse crop, manure, Inoculation, and lime. 



