PLANT GROWTH AND THE AERIAL ENVIRONMENT

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Abstract
Summary: A comparison was made between the rooting conditions used previously in this series of investigations (sandy loam with added fertilizers) and a mixture of vermiculite, sand and gravel with culture solution. The principal effect of vermiculite was to increase the leaf weight by 25% for a given total dry weight. This was mainly compensated for by a lower root weight. The specific leaf area of vermiculite plants was 5% lower than for plants of comparable size and unit leaf rate in sandy loam. The overall result was a rise of 20% in leaf area ratio. The unit leaf rate was unaffected by the rooting condition so there was a resultant 20% increase in relative growth rate over that in sandy loam. The second comparison was with Red light from magnesium arsenate tubes (6000–7000 Å). Red light from germination gave excessively spindly plants, but plants grown initially for 10 days in Daylight‐white grew well subsequently in Red. There was no effect of Red light on leaf weight/total dry weight distribution. The specific leaf area and relative growth rate were marginally lower. Red light was converted 20% more efficiently on an incident energy/apparent assimilation basis.

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