Molybdenum as a factor in the nutrition of lettuce

Lettuce grown in nutrient solution sometimes showed slight benefit on a dry-weight basis from the addition of 0.1 p.p.m. Cr, Sr, Ti or V, while Zn was usually harmful. Addition of Mo at a similar concentration, however, exerted such a marked beneficial effect on both yield and appearance as to suggest that this element was essential for healthy growth. Confirmation of the response was not always obtained, and search was made for some factor which would account for the lack of uniformity in the results. Neither the season of the year, the variety, modifications in the nutrient solution, nor the addition of other trace elements appeared to be responsible, and further work is necessary for the elucidation of the problem.