earlier references are listed there. Also in the transport problem, in Momentum Transfer, Hre. is negligible; see Parikh, J.,4 Appendix B. 6 Allowing A to depend on w2 [see Bardeen, J., Rev. Mod. Phys., 34, 667 (1962), Appendix BI does not affect the main part of our argument, concerned with terms linear in w. 7 Note that, contrary to our notation, the momentum of a quasiparticle of "type 1" (spin-) is called-k in ref. 4. 8 The condition owkF << 1 in equation (16) sets an upper bound to Jv| but still admits fairly large values of In 1vi (.10, say).

Several structural changes in cotton (Gossypium hirsutum L.) leaves attendant on development under conditions of water deficit were examined. Cell size was less and cell wall thickness greater in the leaves of stressed plants than in leaves of well‐watered plants. A short review of the literature suggested that the lesser cell size is a fairly general observation and that it may contribute to plant resistance to moisture stress. A simple model is developed to investigate the influence of the reduction of cell size on cellular water relations. The predictions which can be drawn from simulations with this model are that smaller cells should maintain turgor to lower values of water potential than larger cells. Rather large changes in cell water relations are predicted for small changes in cell size. These effects are related principally to the changing proportion of cell water which resides in the cell wall and is external to the plasmalemma and the osmotic adjustment system. This prediction is in agreement with several observerations on the behavior of stress‐hardened plants and supports the hypothesis that plants or tissues with the smaller cell size will be more tolerant of low water potential.

ABSTRACT

An understanding of the relationship between N assimilation and grain yield and protein, and the measurement of genetic variation in preanthesis and postanthesis N assimilation in wheat (Triticum aestivum L.) are necessary to achieve additional gains in selecting for both high grain yield and high grain protein. Thus, total N assimilation in the spring wheat cultivars ‘Anza’ and ‘Cajeme 71’ and 96 F5‐lines from the cross of these cultivars was studied in field experiments. Freanthesis N assimilation was similar for the two cultivars, but by maturity Anza had assimilated 9% (P < 0.01) more N than Cajeme 71 in both high and low N fertility levels. This difference was mainly due to greater postanthesis assimilation by Anza (22% of total) than Cajeme 71 (10%). Significant genetic variation among F5 lines in N assimilation prior to anthesis occurred in two of three experiments, but no relationships were found between this trait and grain yield, grain protein concentration, or grain protein yield. Significant genetic variability in N assimilation after anthesis was detected, although estimates of heritabilities were low. Nitrogen assimilation after anthesis strongly influenced grain and grain protein yields, explaining 27 to 39% of the variation, but no relationship was found with grain protein concentration. The residuals from the regression of N assimilation after anthesis on biomass at anthesis were also strongly related to grain and grain N yield in a stagewise regression analysis, indicating variation other than random error was involved. Grain protein concentration was also positively associated with these residuals in one experiment. Possible sources of this variation, particularly with relation to roots are discussed. Total N assimilation showed broad‐sense heritabilities of 21 to 27% and was correlated (r = 0.68 to 0.86; P < 0.01) with grain and grain protein yields. Thus genetic variation in N assimilation has a role in determining grain yield and protein concentration in wheat. Further work to determine the genetic and physiological basis of factors influencing N assimilation is needed, especially with regard to roots.

ABSTIRACIThe effect of NaCl and Na2SO salinity on NO3-assimilaon in yonng barley (Horden m vlgare L var Numar) seed was studied. The induction of the NO-tranporter was affected very little the major effect of the salts was on its activity. Both a-and SO42-salts severely inhibited uptake of NO-. When compared on the basis of osmolality of the uptake solutions, a-salts were more inhibitory (15-30%) than S042-salts. At equal concentrions, SO42-salts inhibited NOj-uptake 30 to 40% more tha did a-salts. The absolute concentrabons of each io seemed more important as inhibitors of NOi-uptake than did the osmolality of the uptake solutios. Both KI and Na salts inhibited NO3-uptake similarlr, hence, the process seemed more sensitive to anionic linity than to cationic salinity.Unlike NO3-uptake, NO3-reduction was not affected by salinity in short-term studies (12 honrs). The rte of reduction of endogeos NOiin leaves of seelings gron on NaCl for 8 days decrased only 25%. Nitrte redutase activity in the salt-treated laves also decrased 20% but its activity, determined either in vitro or by the 'amerobic' in vivo assay, was always greater than the actual in sits rate of NOQ reducton.When salts were added to the assay medium, the in vitro enzymic activity was severely inhibited; whereas the anaerobic in vivo nitrate reductase activity was affected only slightly. These results indicate that in sits nitrate reductase activity is protected from salt injury. The susceptibility to injury of the NO-transporter, rather than that of the NO3-reduction system, may be a critical factor to plant survival during salt stress.The assimilation of NO3-, the predominant form of N available in an aerobic environment, is critical if plants are to adapt, grow, and reproduce in saline conditions. Not only is NO3 assimilation required for growth and development, but some of its metabolites accumulate during stress (1 1, 16, 30). It is well known that both proline (1 1, 16, 30) and betaine (10) accumulate during stress. Proline apparently originates from recently formed glutamate (5). Methylated quaternary ammonium compounds and possibly some amino acids accumulating in stressed plants could serve as osmotica for osmoregulation (10,16,30 Stargrass. In contrast, NaCI slinization had little effect on N uptake in winter barley but impaired its incorporation into the protein fraction (13). In leafdiscs ofNicotiana rustica, salt stress reduced both the uptake of L-leucine and its incorporation into proteins (3).The reported effects of salinity on N assimilation are controversial, because no studies were done that measured all of the processes of NO3-assimilation simultaneously. Measuring only uptake or internal reduced N does not yield a balance sheet needed to determine which processes are affected.This report describes the effects of salinity on the processes of NO3-assimilation. MATERAS AND METHODSSeedling Growth. Two varieties of barley (Hordeum vulgare L.), Numar and Arivat, were grown. Numar is a salt-tolerant and Arivat is a salt-sensitive variet...