Experimental researches on vegetable assimilation and respiration.—XVI. The characteristics of subnormal photosynthetic activity resulting from deficiency of nutrient salts

When grown as a series of water-cultures, each deficient in one or other of the essential nutrient salts, plants of Phaseolus vulgaris all show a lowered photosynthetic activity. Comparison of the characteristics of this state with those of the lowered activity, due to old age, suggests that subnormal photosynthetic activity in general depends upon reduction of the effective chloroplast surface, and that the magnitude of this reacting surface must be a factor of fundamental importance in the quantitative determination of assimilation. It is well known that deficiency of nutrient salts retards the general growth of plants, as measured by the increase of dry-weight. Since 90 per cent. of the dry-weight of plants is contributed by the process of photosynthesis, it follows that this retarded growth must result, directly or indirectly, from reduction in the amount of carbohydrate photosynthesized.