The tolerance to chronic high‐temperature stress varies greatly among Kentucky bluegrass (Poa pratensis L.) cultivars. This study of photosynthesis characteristics was conducted to determine whether such traits differ among cultivars and contribute to variable hightemperature tolerance. High‐temperature‐tolerant cultivars exhibited superior growth rates at 30 °C but growth rates were similar among cultivars at 10 °C. At 10 °C, fructosan comprised an approximately two‐fold larger portion of the plant dry weight than at 30 °C, however nonstructural carbohydrate fractions did not differ among cultivars. Under each experimental temperature, the sum of glucose, fructose, and sucrose fractions was approximately the same, though the relative concentrations were temperature dependent. Apparently fructosan served as a buffer fraction that allowed the sum of the other nonstructural fractions to remain constant. Photosynthetic response to increased leaf temperature was similar among cultivars but differed among acclimation temperature regimes. Net photosynthetic rates varied by as much as one‐third among cultivars, however, with a positive relationship between net photosynthetic rates and high‐temperature tolerance. These differences were not attributable to differential CO2 diffusive resistances. This evidence indicated that high‐temperature‐tolerant cultivars were capable of sustaining superior net photosynthetic rates under high but not low temperature conditions. It is suspected that cultivar differences in photosynthetic electron transport capacity may have caused this trend.

Cytokinin treatment is known to promote expansion of light-grown excised radish (Raphanus sativus L. cv Crimson Giant) cotyledons. This expansion, at least in part, seems to be related to an increased accumulation of osmotically active reducing sugars. Kinetin treatment did not cause increased levels of isocitrate lyase activity over the controls, but stimulated increased levels of two invertase forms, designated types I and II. Type I was soluble and type II was insoluble after homogenization in 10 millimolar tris(hydroxymethyl)aminomethane-HCl (pH 7.0). Both types were soluble after homogenization in 300 millimolar NaCI. At low salt concentration, type II was retained on a diethylamioethyl-cellulose column and type I was not. Type II was then eluted from the column at high salt concentration. Types I and II exhibited pH optima of 53 and 43, Michaelis constants of 4.96 and 1.23 millimolar sucrose, and molecular weights of 65,000 and 57,000 daltons, respectively. The kinetin promotion of reducing sugar accumulation may be related to increased levels of the two invertase forms, but is probably not a result of direct cytokinin-stimulated glyoxysomal activity.

A hydroponic system has been devised for the culture of large numbers of grass plants to be used in subsequent physiological experiments. This system is inexpensive to construct, requires minimal maintenance, and can be left unattended for several days. Plants produced by this method are of uniform size and are easily harvested and cleaned.