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Development of Photosynthesis in Cotton Seedlings, Gossypium hirsutum L.¹

An infrared gas analyzer was used to follow CO₂ exchange (dark respiration and net photosynthesis) through the first 248 hr of germination of cotton seeds. The following events were noted: (a) dark respiration was first detectable 6 hr after placing the dry seed in water (planting); (b) the photosynthetic cempensation point was reached 86 hr after planting and 24 hr after emergence and occurred during the unfolding of the cotyledonary leaves; (c) maximum rates of net photosynthesis (33 mg CO₂/dm²/hr at 64.8 kilolux with 500 ppm CO₂) were attained by 200 hr after planting and remained at this level during the remainder of the test period (48 hr); and (d) photosynthetic rates increased as light and CO₂ concentrations were increased. The fully expanded cotyledonary leaf stage (200 to 248 hr after planting) of the cotton seedling is suitable for photosynthetic studies cause of the stability and uniformity of the photosynthetic rate.

General Electric Cool Beam lamps were found to be equally as effective as sunlight in providing energy for fixation of CO₂.

Dark respiration rates, determined throughout the experiment, increased from 0 to a maximum by 120 to 130 hr after planting and remained constant for the next 24 hr.

² Professor of Agronomy, Agriculture Division, Arizona State University, Tempe, Ariz.

Received for publication March 28, 1966.