1917] FIELD CROPS. 527 



however, appearing relatively indifferent. Silver and copper v?ere very un- 

 favorable to growth, mercury less injurious, and lead and iron salts the least 

 hurtful to vegetative growth. Low concentrations of the nutritive components 

 hastened spore formation. 



Note on the nitrog-en nutrition of mold fungi, W. Brenneb (Centbl. Bakt. 

 letc], 2. AM., 44 {1915), No. 9-lS, pp. 304, 305).— Besides a few corrections and 

 comments on statements made in the previous article (E. S. R., 32, p. 327), a 

 few additions, of contributions not later than 1913, are made to the bibliography 

 previously given. 



Variations in nodule formation, L. T. Leonabd {Jour, Amer. Soc. Agron., 

 8 {1916), No. 2, pp. 116-118).— In view of the observed differences in the degree 

 of inoculation exhibited by legume varieties, and even by individual plants, ex- 

 posed to the nodule-forming organism, the author tested 19 varieties of soy 

 beans with cultures taken from one of them. He obtained nodules in case of 

 each variety, only one requiring a third inoculation. 



The present state of our knowledge of the physiological significance of the 

 mycorrhizae of trees, D. L. Petri {Intemat. Inst. Agr. \_Rom,G\, Mo. Bui. Agr. 

 Intel, and Plant Diseases, 6 {1915), No. 9 pp. 1138-1151). — The author concludes 

 a review of the studies and views of various authors regarding the real nature 

 of the relations between the roots of trees and the mycorrhizre found in con- 

 nection therewith by stating that the results of 30 years of scientific research, 

 at least so far as arborescent plants are concerned, have not led to either con- 

 firmation or rejection of the theory of mutuality. 



FIELD CROPS. 



The use of checks and repeated plantings in varietal tests, F. J. Pkitchabd 

 {Jour. Amer. Soc. Agron., 8 {1916), No. 2, pp. 65-81, figs. 3). — This article is a 

 discussion of the methods used in field-variety tests. The experiments were 

 conducted with sugar beets in an attempt to determine three things: (1) The 

 optimum frequency of checks; (2) whether the best frequency of checks is 

 efficient enough for satisfactory comparisons; and (3) the measure of the com- 

 parative effect of repeated plantings upon the experimental error. The results 

 are discussed in detail, and the general conclusions drawn are as follows: 



(1) The practice of dispensing with check rows and using the mean of all 

 progeny rows as a standard of comparison appears to be less efficient than 

 the employment of frequent checks; (2) check rows 32 in. from the prog- 

 eny row varied less than those 64, 96, 128, and 160 in. distant; when the 

 probable error was duly taken into account the last four distances appeared to 

 be good checks; (3) the use of alternate rows as checks did not offset the 

 variability in yield due to irregularities of the soil; and (4) the experimental 

 error was reduced about 50 per cent by means of 10 replications and alternate 

 check rows. 



The mode of pollination in some farm crops, M. N. Pope {Jour. Amer. Soc. 

 Agron., 8 {1916), No. 4, pp. 209-227) .—This article is a review of the literature, 

 com, wheat, oats, barley, rice, rye, and flax being discussed specifically. A 

 bibliogi-aphy of the literature cited is included. 



The identification of grasses by their vegetative characters, L. Cabeieb 

 {U. S. Dept. Agr. Bui. 461 {1917), pp. 30, figs. 60).— Following the work of other 

 investigators the author presents a plan of classification to identify grass 

 seedlings based somewhat on that of Percival (E. S. R., 12, p. 719), but includ- 

 ing a larger number of gi-asses. The botanical characteristics of grasses before 

 the blooming stage are described and the use of the key discussed. 



