Vegetable Plant Part Relationships. III. Modification of Carrot (Daucus carota L.) Root and Shoot Weights by Gibberellic Acid and Daminozide

Aqueous foliar sprays of N-dimethylaminosuccinamic acid (daminozide)at 2000 p.p.m. and gibberellic acid (GA) at 100 p.p.m. wereapplied 45, 59, 82 and 100 days after sowing to Chantenay carrotswith population densities of 244, 495 and 883 plants m^–2.The plants were harvested on ten approximately weekly occasions;fresh weights were determined and d. wt estimates were obtainedfor the separated shoots (s) and roots (r). Allometric linearregressions of the logarithm of s on that of r at each harvestseparately, clearly showed that GA always increased shoot: rootratio and reduced root yield (by approximately 35 per cent)but could sometimes also increase whole-plant weight. Daminozideincreased root yield (by approximately 7 per cent from 80 tonnesha^–1) and tended to have effects opposite to those ofGA. Daucus carota L., carrot, root weight, shoot weight, N-dimethylaminosuccinamic acid (daminozide), gibberellic acid     

Carbon Economy of Carrots During Initiation of the Storage Root in Cultivars Contrasting in Shoot: Root Ratio at Maturity

Photosynthesis, respiration and growth of two cultivars of carrotwith contrasting ratios of shoot: storage root weight at maturity,were compared during initiation of the storage root at 20 °C.Partition of assimilate between shoot, roots and respirationshowed no varietal differences but distribution between storageand fibrous roots was different from the time that the storageroot could be morphologically identified. For both cultivarsover the period investigated, approximately 64% of net photosynthesiswas partitioned to the shoot with 5% lost as respiration duringthe dark and 59% used in growth. Of that exported to the rootsystem (36%), 19% (of net photosynthesis) was used in growthand 17% was lost in respiration. In the cultivar with greatershoot: storage root ratio at maturity, 4.6% was allocated tothe storage root in contrast to 7.5% in the cultivar with alesser shoot: storage ratio at maturity. It is concluded thatgreater dry matter accumulation in the storage root of the lattercultivar does not result from transient differences in respiratoryloss and is not evident in shoot to total root dry matter distributionover this period. Daucus carota L, carrot, assimilate partition, shoot, storage root, shoot: root ratio     

Some Physiological Characteristics of Two Tomato Cultivars, One Tolerant and One Susceptible to Tobacco Mosaic Virus

A comparison was made of physiological activity in the tomatocv. Potentate, susceptible to tobacco mosaic virus (TMV) withthat in cv. Virocross which is tolerant. Growth analysis overa 5-week period showed Potentate to have a higher relative growthrate and a higher net assimilation rate than Virocross. In reciprocalgrafts scion growth, including dry weight, was greater on Potentaterootstocks than on Virocross. Growth responses were studiedin these grafts following foliar sprays of N-6 benzyladenine(BA) and gibberellic acid (GA). The response of the scion toGA was similar in both cultivars and there was no interactionbetween GA and rootstock for scion growth. An interaction betweenstock and BA was found for leaf growth. Bleeding sap from Virocross contained more gibberellins, morecytokinins, and a lower concentration of amino compounds, especiallynon-protein acids, than Potentate. There were more gibberellinsin the roots of Potentate but no difference between shoots ofthe two cultivars. In reciprocal grafts TMV multiplied more rapidly in Virocrossscions on Potentate rootstock than on their own, but Virocrossstocks did not affect virus multiplication in Potentate scions.Spraying Potentate plants with BA reduced the rate of virusmultiplication. It is suggested that virus multiplication in the shoot may becontrolled by two distinct root factors, viz, the supply ofnative cytokinins and the amount and nature of the nitrogenouscompounds which directly influence the rate of shoot growth.     

The Rate of Growth and Partitioning of Assimilates in Young Grass Plants: A Mathematical Model

A model describing the increase in weight with time of younggrass plants is formulated. The parameters are the relativegrowth rates of the root and shoot systems; k, the ratio ofthe relative growth rate of the root system relative to thatof the shoot system; b, the weight of the root system when thatof the shoot system is unity, and u the rate of increase inweight of the whole plant per unit of shoot system per unitof time, k and b are the constants in the allometric formula,r = bs^k where r and are the weights of the root and shoot systems.The model enables the effect of changes in the distributionof assimilates between the root and shoot systems upon the rateof growth of the plant to be assessed. Data from a number ofexperiments are analysed in this manner and the significanceof the results discussed.     

A Comparative Study of the Effects of Some Growth Regulators on the Biochemistry of Oryza sativa L.

A comparative study was made on the effects of indol-3yl-aceticacid (IAA), maleic hydrazide (MH), naphthalene acetic acid (NAA),and gibberellic acid (GA) at a concentration of 1o^-1 mg I^-1,on the growth and metabolism of Oryza sativa L., cv. Bhasamanik.All the growth substances excepting NAA caused promotion ofroot elongation and increased the number of roots formed buthad very little effect on shoot growth. NAA was found to havea retarding effect on the general growth of the plant, but alsoincreased the number of roots formed. At the concentration used IAA caused enhanced protein synthesisin parallel with increased root growth. However, with MH nosuch direct relationship could be observed between root growthand protein synthesis at the early stage, but stimulation ofroot growth was directly related to increased protein synthesisat the later stage. Despite the adverse effect of NAA on thegrowth of the plant, protein synthesis was not affected. Infact a general increase in the protein content of the plantwas observed. In plants treated with GA increased sugar contentand enhanced protein synthesis were noted. The levels of free amino acids were found to be affected markedlyby the application of the growth regulators. With NAA treatmentan accumulation of asparagine in the shoot and with GA an increasein the level of alanine in the root were noted. Aspartic aciddecreased in the roots, but increased in the shoots of treatedplants. Glutamic acid was lower in plants treated with IAA,MH, and NAA, while treatment with GA increased it in the shootat the tillering stage. In the shoots of IAA-, MH-, and NAA-treatedplants an increase in the quantity of serine was noted whereasunder the action of GA both serine and glycine decreased.     

The Effect of Photon Flux Density and Duration of the Photosynthetic Period on Growth and Dry Matter Distribution in Carrot

The distribution of dry matter between shoot and storage rootof carrot plants grown in light regimes varying in intensity,duration and integral, is used to test an hypothesis for thecontrol of assimilate partition Results from seven varietiesshow that shoot to storage root weight ratios are affected bythe light environment, but that these effects are associatedwith the effect of light on plant size It is concluded thatquantitative alterations to the supply of assimilate, resultingfrom variation in the light regime, do not affect its partitionto different organs This is discussed in relation to other investigationswhich have suggested a relationship between the duration ofthe photosynthetic period, assimilate sequestration in foliarstarch and partition between shoot and root Daucus carota L, carrot, assimilate partition, light intensity, daylength, shoot, storage root, shoot-root ratio, source-sink relations     

Storage Organ Development in Radish (Raphanus sativus L.). 2. Effects of Growth Promoters on Cambial Activity in Cultured Roots, Decapitated Seedlings and Intact Plants

The radish varieties Cherry Belle and Long White Icicle wereused to investigate the role of the shoot and the effects ofsynthetic growth promoters in controlling cambial activity inthe seedling axis. Development was compared in excised roots, roots with hypocotylsattached and intact seedlings cultured aseptically on a nutrientmedium. No cambial divisions were seen in isolated radicleswhich had been cultured for ten days following excision butretention of hypocotyl tissue or the entire shoot resulted incambial activity and the production of secondary vascular tissues.Enriching the culture medium by raising the sucrose conantrationto 8% and including 10^–5 M indol-3yl acetic acid (IAA)5 x 10^–6 M 6-benzylaminopurine (BA) and 5 x 10^–4Minositol enhanced root thickening, increasing stele and xylemdiameters in roots cultured both with and without attached shoottissues. The effects of shoot tissues and enrichment of themedium were additive. The effects of auxin, cytokinin and gibberellin (gibberellicacid, GA²) were also studied on daxpitated seedlings. BA wasmuch more effective in inducing cell divisions in the hypocotylthan either IAA or GA supplied separately but a mixture of IAA+GAalso produced clearly defined arcs of cambial tissue. Littlesecondary tissue had been produced after seven days' treatment,and stelar enlargement was due to the development of a cambialzone and cell expansion in the primary tissues. Only minor differencesin response were observed between the two varieties. No stimulation of storage organ development occurred when auxin,cytokinin or inositol was inwrporated into the inorganic culturesolution in which plants of Cherry Belle were grown. Rnphanus sarivus, radish, storage organ, cambial activity, growth promoters, indol-3-ylacetic acid, 6-benzylaminopurine, gibberellic acid     

The Role of Roots in Control of Bean Shoot Growth

Restriction of root growth by growing bean plants (Phaseolusvulgaris L.) in very small pots led to the development of dwarfplants. The leaves of those plants were smaller and their internodesshorter than those of control plants which were grown in largerpots and had developed a more extensive root system. A largequantity of starch—much more than in control plants —accumulated in the leaves and shoots of the dwarf plants. Increasingthe amount of minerals which was supplied to the roots, enhancedleaf growth of the control plants but failed to affect the dwarfones, in spite of the fact that in both cases the treatmentincreased the content of N, P and K in all the plant organs.The leaf water content was similar in both treatments, but theleaf water potential was higher in the dwarf plants. Exogenousapplication of gibberellic acid (GA₃) to the dwarf plants overcamethe reduction of stem growth completely, and that of the leavespartially. Application of the cytokinin, benzyladenine (BA)did not affect stem growth, but increased that of the primaryleaves. A combined supply of GA₂ + BA restored completely thegrowth of the stem and the primary leaves, and partially thatof the trifoliate leaves. It is concluded that a limited rootsystem restricts shoot growth through an hormonal system inwhich at least gibberellins and cytokinins are involved, andthat the dwarfing is not a consequence of mineral or assimilatedeficiency, or due to water stress. Phaseolus vulgaris L., leaf growth, stem growth, root restriction, gibberellic acid, benzyladenine, cytokinin     

Morphogenetic Responses to Gibberellic Acid of a Radiation-induced Mutant Dwarf in Groundsel, Senecio vulgaris L.

A dwarf mutant of Senecio vulgaris L. induced by gamma radiation,which differs from the wild-type by a single recessive gene,grew as tall as the wild-type plant, and almost five times astall as dwarf control plants when treated at weekly intervalsfrom the seedling stage with 10 p.p.m. gibberellic acid. Thewild-type groundsel responded only slightly to similar treatment.Some evidence was obtained that the response to GA was relativilygreater when plants were grown during the late autumn. Dwarfnessin the mutant is due to fewer as well as to shorter internodes;the rate of leaf initiation is reduced, but the onset of thereproductive phase and the duration of the life-cycle are notaffected by the mutation. Gibberellic acid leads to a conspicuouselongation of the internodes intreated dwarf plants, but notalways to a significant increase in their number. An increasein the dry weight of treated plants was observed, and this wasshown to be due to an increase in photosynthetic area and notto increased photosynthetic efficiency. Comparative observationsof shoot morphogenesis in wild-type and dwarf groundsel. andin dwarf treated with gibberellic acid, have shown that thetype of shoot development induced by gibberellic acid in dwarfplants does not correspond exactly to the normal mode of developmentin wild-type plants. Increased mitotic activity in the subapicaltissue of the mutant following gibberellic acid treatment resultedin greater and earlier elongation of the internodes. However,the typical form and dimensions of the wild-type plant werenot wholly restored.     

Developmental Physiology of Sugar-beet: IV. EFFECTS OF GROWTH SUBSTANCES AND DIFFERENTIAL ROOT AND SHOOT TEMPERATURES ON SUBSEQUENT GROWTH

The effects of three growth substances, viz. indol-3yl-aceticacid (IAA), gibberellic acid (GA₃), and kinetin (KIN), and differentialshoot and root temperatures on growth of sugar-beet (Beta vulgarisL.) plants have been studied. IAA, GA₃, and KIN were applied in aqueous lanolin at differentconcentrations (50 ppm to 5000 ppm) to decapitated sugar-beetplants at the eight-leaf stage, one group also having alternateleaves removed. The growth substances significantly increasedthe dry weights of the plants when all the leaves were present,which was mainly explained by the large increase in roots. Thegrowth substances probably stimulated cambial activity and hencethe mobilization of substrates resulting in a bigger root whena relatively large leaf area existed. The failure of the plantsto respond to treatments following the removal of alternateleaves suggests that under such conditions the growth substanceshave hardly any major effect on the production of substrates;rather they influence growth by regulating the movement of substratesby altering the ‘sink strength’ if the supply ofsubstrates is not limiting. It could also be that the rootsproduce sufficient growth substances to maintain half the leavesat maximum expansion and maximum photosynthesis. Treatment withgrowth substances would therefore have little effect. When allthe leaves were present, they are limited by insufficient growthsubstances. All combinations of root and shoot temperatures of 17 and 25°C were imposed on plants decapitated at the eight-leafstage, one group also having each alternate leaf removed. Leaf8 expanded most at shoot and root temperature of 25 °C whereasother leaves had the largest areas at shoot and root temperatureof 17 °. When all the leaves were present root growth wasmaximal at shoot temperature of 17°C and root temperatureof 25 °C, but when alternate leaves were removed maximumroot growth occurred at shoot and root temperatures of 25 °C.Generally, a higher concentration of soluble carbohydrates wasfound in the roots and leaves when either the shoot or rootor both were kept at 17 °C. Concentrations of nitrogen,phosphorus, and potassium in different organs were less at 17°C than at higher shoot or root temperatures and decreasedwith age.     

Dry Matter Distribution Between the Shoot and Storage Root of Carrot (Daucus carota L.): II. Effect of Foliar Application of Gibberellic Acid

The effects of foliar sprays of gibberellic acid (GA) on drymatter distribution in carrots were investigated in three fieldexperiments between 1977 and 1979. The results were interpretedby using a simple quantitative model of assimilate partitioningbetween storage root and shoot. Although the response to GAvaried depending on the year in which the experiment was done,the model successfully described the effects of spraying time,GA concentration, planting density, plant age and cultivar.The maximum effects on repartitioning were achieved with concentrationsof 100–500 mg 1_–1 GA and, except for very earlyor late sprays, the effect was constant with time over a roughly4-week period. The multiplicative nature of the model was usefulin that despite the occurrence of various interactions, a similarassimilate partitioning response to GA in all four cultivarswas demonstrated. The model did not suggest an explanation forthe seasonal effects. Daucus carota L., carrot, assimilate distribution, dry matter distribution, storage root, gibberellic acid, partitioning model     

The Effects of Infection by Rust (Puccinia lagenophorae Cooke) on the Growth of Groundsel (Senecio vulgaris L.) Cultivated under a Range of Nutrient Concentrations

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae Cooke, was grown at a rangeof nutrient concentrations in sand culture. There were statisticallysignificant interactions between the effects of infection andnutrient supply upon the dry weights of stems, leaves, rootsand reproductive tissues, leaf area and cumulative capitulumproduction. This interaction occurred since infection causedsignificant inhibitions of growth only at moderate or high nutrientconcentrations. At low concentrations rusted plants were similarto or slightly larger than controls. Both in controls and rustedplants root: shoot ratios increased as nutrient supply declined.The ratio of root: shoot dry weight was consistently reducedby infection whilst root length: leaf area ratio was relativelyunchanged. More detailed investigations confirmed that infection had littleeffect on plant growth under nutrient deficient conditions despitesuppression of the host's ability to increase root: shoot ratiosin response to nutrient stress. This reflected the inhibitionof relative growth rates in rusted plants at high but not lownutrient concentrations, which in turn reflected reduced netassimilation rates (NAR). Increases in leaf-area ratio (LAR)often ameliorated the decline in NAR in rusted plants. Senecio vulgaris L., Puccinia lagenophorae Cooke, nutrient deficiency, growth, root: shoot ratio     

Analysis of Dry Matter Partitioning in Dactylis glomerata during Vegetative Growth Using a Carbon Budget Model

The dry matter partitioning in vegetative plants of Dactylisglomerata was studied from experiments performed in controlledenvironments. Plants were grown hydroponically in growth chambers,at two constant temperatures (17 and 25 °C). In both experimentsthe root fraction decreased regularly with time, an effect thatwas more accentuated in the higher temperature regime. In orderto explain the change in dry matter partitioning, the experimentalshoot and root growth were analysed using a carbon budget modelwhich includes shoot and root maintenance requirements. Themodel predicts a relationship between the root specific growthrate and the product of shoot specific growth rate and shootto root dry weight ratio. In the range of experimental accuracy,this relationship was found to be linear at both temperatures,which should indicate that the partitioning coefficients andthe root maintenance coefficient remained constant during vegetativegrowth. The effect of temperature on the value of these coefficientscan be specified from a linear regression analysis. Between17 and 25 °C, the root maintenance coefficient increasedby about a factor of two, whereas the partitioning coefficientsdid not vary significantly. On the basis of these results, itwas shown that the decrease in root fraction during vegetativegrowth should be mainly attributed to the decrease in net specificactivity of shoots.Copyright 1994, 1999 Academic Press Dactylis glomerata L., vegetative growth, model, partitioning, root:shoot ratio, shoot specific activity, maintenance requirements     

The Effect of Phosphorus Nutrition upon the Growth and Morphology of Young Plants of Lolium perenne L.

Genotypes of Lolium perenne were grown in soil of low phosphorusstatus, with and without additional phosphorus. Lack of phosphorusresulted in a great reduction in the number of main roots andin an increase in the length of each individual root. The numberof tillers was also reduced, but to a lesser extent than thenumber of main roots. The dry weight of the root and shoot systemwas reduced to a lesser extent than the numbers of roots andtillers. The effect on root relative to shoot growth variedwith the genotype.     

Nitrogen Uptake and Plant Growth II. An Empirical Model of Vegetative Growth and Partitioning

An empirical model of vegetative plant growth is presented.The model is based on experimental data on Polygonum cuspidatum,which showed (1) that the partitioning of dry matter and nitrogenamong organs was linearly related to the nitrogen concentrationof the whole plant and (2) that leaf thickness was negativelycorrelated with leaf nitrogen concentration. The model properlydescribes the behaviour of plants. Steady-state solutions ofthe model give the relative growth rate, specific leaf weight,and partitioning of dry matter and nitrogen among organs withthe net assimilation rate and the specific absorption rate asenvironmental variables. The effect of nitrogen removal on drymatter and nitrogen partitioning was examined as non-steady-statedynamic solutions of the model. The model predicted not onlyreduced leaf growth and enhanced root growth but also a fluxof nitrogen from the leaf to the root, which agreed with theexperimental results. Mathematical model, partitioning of dry matter and nitrogen, plant nitrogen, relative growth rate, shoot: root ratio, specific leaf weight     

In vitro Growth of Vegetative Tomato Shoot Apices

Explants from the shoot apex of the tomato, comprising the apicaldome and youngest primordium together with small amounts ofsub-apical tissue were cultured for periods of 1 to 4 plastochrons.By the use of a simple parameter, the axillary distance, thegrowth-rate could be accurately monitored throughout each plastochron. Gibberellic acid, coconut milk, and kinetin, in addition tosucrose and inorganic salts, all promoted growth of the apex;a combination of gibberellic acid and coconut milk gave thefastest growth. Temperature had a large effect on the growth-ratewith an in vitro Q₁₀ of 2.1 contrasted with an in vivo Q₁₀ of1.2 over the range of 15 to 25 ?C. On gibberellic acid and coconutmilk at 15 ?C two-thirds of the in vivo growth--rate was sustainedin culture for two plastochrons after which the growth-rategradually declined; at 20 and 25 ?C growth-rates slightly higherthan in vivo rates were sustained for 1 plastochron before amore rapid decline. The anatomy of these in vitro apices wasnormal for 1? plastochrons after which there were small increasesin cell volume in the developing primordium. Reducing the amount of sub-apical tissue drastically reducedthe growth rate but had little effect on the responses to gibberellicacid and coconut milk. Explants are considered to be useful material for studying thechanges that take place in the apex during the course of 1 or2 plastochrons, but inadequate on the media tested for experimentsinvolving longer periods of growth. Explants also provide asensitive assay system for the effects of growth factors onthe rate of shoot apical growth.     

Growth regulator effects on storage root development in carrot

The major carbohydrates stored in carrots are sucrose, glucose and fructose. The ratio of sucrose to reducing sugars varies between cultivars, with early forcing types generally having a higher level of reducing sugars while storage types have a greater proportion of sucrose.In an early forcing cultivar, Super Sprite, high acid invertase activity was correlated with low levels of stored sucrose. As acid invertase activity decreased, the levels of reducing and non-reducing sugars appeared to be related to a balance between alkaline invertase and sucrose synthetase activities.Foliar applications of gibberellic acid at 35 and 42 days after sowing reduced the root/shoot ratio while similar applications of chlormequat chloride marginally increased the ratio. Both growth regulators temporarily increased sucrose stograge, but only gibberellic acid consistently reduced hexose accumulation.Gibberellic acid reduced acid invertase activity following both applications while only reducing the activities of sucrose synthetase after the first application and alkaline invertase after the second application, respectively. Chloremequat chloride increased acid invertase activity after the first application but otherwise has no effect on the activities of the enzymes studied. The significance of changes in assimilate partitioning are discussed in relation to published schemes on carbohydrate storage in root vegetables.     

PHYSIOLOGICAL ACTIVITIES OF HELMINTHOSPOROL AND HELMINTHOSPORIC ACID: I. EFFECTS ON GROWTH OF INTACT PLANTS

Helminthosporol (H-ol) and helminthosporic acid (H-acid) wereeffective in promoting elongation of leaf sheaths of rice, Japanesebarnyard grass and dwarf maize (d-2 and d-5) and of hypocotylsof taisai (Brassica chinensis), but inactive in leaf sheathsof oat and wheat, hypocotyls of sesame and morning glory (Pharbitisnil) and epicotyls of Pharbitis and dwarf and tall peas. Onthe elongation of the leaf sheath of maize d-1, H-ol was promotivebut the activity of H-acid was doubtful. On hypocotyls of lettuceand daikon (Raphanus sativus), only H-acid was active. Multiplicationrate and size of fronds of Lemna perpusila were not affectedby either of the substances. Compared with gibberellic acid for the effect on the shoot growth,H-ol and H-acid were weak in activity and narrower in the scopeof plants that responded. H-ol and H-acid characteristicallypromoted the elongation of the primary root. Comparative effectivenessof H-ol and H-acid varied with plant species or parts examined. ¹ This study was supported in part by grant-in aid of the Ministryof Education (No. 0417). The results reported here were presentedat the Annual Meeting of the Botanical Society of Japan at Kanazawain 1964 (S).     

The Significance of Root Starch in Post-fire Shoot Recovery of the Resprouter Stirlingia latifolia R. Br. (Proteaceae)

Stirlingia latifolia, a common shrub of Banksia woodlands ofSW Australia, is a highly successful resprouter species recoveringfrom fire by multiple sprouting of new shoots from its upperroot stock. in comparison with the congeneric fire-sensitive(obligate seeder) species Stirlingia tenuifolia it exhibitsa low shoot:root dry weight ratio and high concentrations ofstored starch in the cortical tissue of its roots. The relationshipbetween root reserves of starch and development of newly sproutingshoot material following fire is examined in S. latifolia afterspring and summer burns. During the initial 2-5 month periodafter fire, levels of stored starch in the roots fall by 50-75%,followed by a slow increase as plants reproduce and the attainmentof pre-fire starch levels by 1·5-2 years after the fire.Starch reserves of roots can be further reduced by shading theregenerating shoots to limit their input of photosynthates andalmost totally eliminated by monthly removal of successive flushesof new shoots over a 10-12 month period. New shoots continueto sprout until all the starch is eliminated. The data are discussedin relation to the fire-induced reproduction of S. latifoliaand its ability to thrive in very frequently burnt habitats.Copyright1993, 1999 Academic Press Fire response, Proteaceae, resprouter, shoot:root ratio, starch storage, Stirlingia latifolia     

Studies in the Growth of Young of Pinus sylvestris L.: I. The Annual Cycle of Assimilation and Growth

The annual cycle of growth in plants of P. sylvestris L. varyingin age from 2 to 5 years was studied mainly by following theirweight changes through periodic sampling. Immediately followingbud-break there was a period of about 1 month in which, althoughmeristematic and extension growth were rapid in both shoot androot, there was no gain in weight by the plant. There was evidencethat the needles remaining from previous years contained a considerableamount of storage material which was utilized at this time.During May and June the main increase in weight was in the newshoots, but in August and September assimilates were more evenlydivided between the new shoots on the one hand, and the oldstem and the root on the other. The average relative growth-ratesfor the months May to September were between 1·0 and0·4 per cent, per day in plants growing in favourableconditions, the lower rates being found in older plants. Duringthe months October to March slow increase in weight occurredin needles, stem, and root, and the R.G.R.s in two experimentswere 0·21 and 0·15 per cent, per day. The netassimilation rate fell with increasing age and in the summerof the fifth year was 0·06g./g./week or 0·10g./dm.²/week.This low value of N.A.R. is discussed in relation to the knownhigh rate of production of P. sylvestris stands and their evergreenhabit.