As fi part of a broader study, two experiments were carried out in growih chambers with three day/might temperature regimes (10'7, 20/14 and 30,'2rC) sttid>ing growth characteristics of individual seedlings over afour-week period. Experiment 1 was performed with spring barley {Hordeum vulgare L.), Gakopsis tetrahit L., and Viola Arvensis Murray. Experiment 2, with three irradiance levels at 20i'14°C, and one irradiance level at the other temperatures, was performed with spring harley, V. arvensis, Chenopodium album L., Brassica rapa L. ssp. oleifera (DC.) Metzger, and Stellaria media (L.) VUl. Leaf area, dry weight, relative growth rate, net assimilation rate, and net piotosynthetic rate generally showed an optinwim at 20/14''C. Increasing inadiaoce resulted in a decreased specific leaf area. Expressed as fraction of shoot dry weight, green leaves decreased and stems, flowers, and yeflow leaves increased with iacreased time, irradiance, and temperature. At all temperatures, barley, B. rapa and G. tetrtdiit had the largest drj' weights, but at 20/14°C C albtm and S. media and at 3OQ1°C C album also had iai^e values. Differences in dry weight between spedes correlated more to morphological features than to assimilation rate.

Summary As a part of a broader study, two experiments were carried out in growth chambers with three day/night temperature regimes (10/7, 20/14 and 30/21^C) studying growth characteristics of individual seedlings over a four‐week period. Experiment 1 was performed with spring barley (Hordeum vulgare L.), Galeopsis tetrahit L., and Viola Arvensis Murray. Experiment 2, with three irradiance levels at 20/14^C, and one irradiance level at the other temperatures, was performed with spring barley, V. arvensis, Chenopodium album L., Brassica rapa L. sspoleifera (DC.) Metzger, and Stellaria media (L.) Vill. Leaf area, dry weight, relative growth rate, net assimilation rate, and net photosynthetic rate generally showed an optimum at 20/14^C. Increasing irradiance resulted in a decreased specific leaf area. Expressed as fraction of shoot dry weight, green leaves decreased and stems, flowers, and yellow leaves increased with increased time, irradiance, and temperature. At all temperatures, barley, B. rapa and G. tetrahit had the largest dry weights, but at 20/14^C. C album and S. media and at 30/21^C C. album also had large values. Differences in dry weight between species correlated more to morphological features than to assimilation rate.