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CLARK are dependent on temperature. In the 100-120°r ange there was no noticeable temperature dependence, so it may be that in the lower temperature range (65-100°) equilibrium was not reached. Such a situation might lead to curvature of the In fnet or In Gorr vs. l/ plots. Further studies should be made to determine the exact nature of the temperature dependence.Because in this study determinations of thermodynamic quantities depend on retention time and retention volume, and because retention data depend directly on the flow rate of the carrier gas, it is important to ascertain that the thermodynamic quantities as determined here are not functions of flow rate. In the general experiments a flow rate of 25 ml/min was used. For three compounds experiments were made in which each compound was studied at flow rates of 20, 25, and 30 ml/min. Though retention times vary widely with flow rate, as expected, the corrected retention volumes were remarkably constant for a given temperature, so that Gibbs energies of adsorption as derived from corrected retention volumes will not be dependent on flow rate. Heats of adsorption were observed to vary only slightly within experimental error, for different flow rates.

G r o w t h a n d P, K, Ca, Mg, Mn, Zn, Fe, a n d Cu c o n c e n t r a t i o n s a n d c o n t e n t s were d e t e r m i n e d in A l -t o l e r a n t a n d A l -i n t o l e r a n t corn (Zea mays L.) i n b r e d s w h e n grown a t v a r i o u s levels of A1. B57 was more t o l e r a n t to A1 t h a n was Oh40B. R e l a t i v e l y low A1 levels (up to 5 rag/l) e n h a n c e d 1357 g r o w t h b u t i n h i b i t e d O h 4 0 B growth. W i t h few exceptions, O h 4 0 B root a n d leaf conc e n t r a t i o n s of t h e elements decreased w i t h a d d e d A1. T h e decreases in elem e n t c o n c e n t r a t i o n s were n o t as large for B57 as t h e y were for Oh40B. T h e Mg c o n c e n t r a t i o n s a n d c o n t e n t s decreased more t h a n t h e o t h e r e l e m e n t s in all i n b r e d s w i t h a d d e d A1. R o o t Mg decreased more t h a n leaf Mg. T o t a l u p t a k e of some e l e m e n t s were h i g h e r at low A1 t h a n w i t h no A1. I n a s m u c h as Mg h a s a p r o n o u n c e d effect on root growth, low Mg m a y be a n i m p o r t a n t response in p l a n t s sensitive to A1. * Journal article No. 82-75 A n d r e w , C. S., J o h n s o n , A. D. and S a n d l a n d , R. L., Effect of aluminium on the growth and chemical composition of some tropical and temperate pasture legumes. Aust. J. Agr. Res. 24, 325-339 (1973).

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