Slow rehydration improves the recovery of dried bacterial populations.

Slow rehydration of bacteria from dried inoculant formulations provided higher viable counts than did rapid rehydration. Estimates were higher when clay and peat powder formulations of Rhizobium meliloti, Rhizobium leguminosarum biovar trifolii, and Pseudomonas putida, with water activities between 0.280 and 0.650, were slowly rehydrated to water activities of approximately 0.992 before continuing the dilution plating sequence. Rhizobium meliloti populations averaged 6.8 x 10(8) cfu/g and 1328 cfu/alfalfa seed greater when slowly rehydrated from bulk powder and preinoculated seeds, respectively. Bulk powder samples were slowly rehydrated to 0.992 water activity by the gradual addition of diluent, followed by a 10-min period for moisture equilibration. Preinoculated seed samples were placed in an environmental chamber at 24 degrees C with relative humidity greater than 80% for 1 h to allow moisture absorption. "Upshock," osmotic cellular stresses that occur during rehydration, was reduced when dried microbial formulations were slowly rehydrated and equilibrated before becoming fully hydrated in the dilution plating sequence. These procedures may also be applicable when estimating total viable bacterial populations from dried soil or other dry formulations.     

Effect of glycerol level in Tris-basek extender and equilibration period on quality of frozen goat semen

Twenty ejaculates, 4 from each of 5 native goats, were collected using an artificial vagina, and the effects of glycerol level (4, 6.4 and 9 %) and the equilibration period (1, 3 and 5 h) were studied by split-sample technique. The extender used was Tris egg yolk citric acid fructose glycerol extender. The semen was frozen in 0.5-ml French straws by exposure for 10 min to liquid nitrogen vapor, 5 cm above the liquid nitrogen level. After 14 h of storage in liquid nitrogen, the straws were thawed in water at 37 degrees C for 12 - 15 sec. The percentage of progressively motile sperm (PPM) and the percentage of damaged acrosomes (PDA) were studied after equilibration and after thawing. The mean PPM after thawing was found to be 64.0 +/- 0.90, 66.92 +/- 0.54 and 63.65 +/- 1.07 when semen was frozen with 4, 6.4 and 9 % glycerol and 61.48 +/- 0.81, 65.05 +/- 0.78 and 68.03 +/- 0.87 in 1-, 3- and 5-h equilibrated semen, respectively. The mean PDA after thawing was 7.12 +/- 0.88, 8.23 +/- 0.76 and 10.58 +/- 0.84 when semen was frozen with 4, 6.4 and 9 % glycerol and 7.0 +/- 0.74, 9.0 +/- 0.95 and 9.93 +/- 0.81 in 1-, 3- and 5-h equilibrated semen, respectively. Both PPM and PDA differed significantly (P<0.01) between glycerol levels, between equilibration periods and between stages (after equilibration and after thawing). The PPM also differed significantly due to equilibration period x stage interaction (P<0.01) and glycerol level x stage interaction (P<0.05). The PDA did not differ significantly due to interactions. When the differences between pairs of means were tested by least significant difference, it was found that after equilibration PPM was not significantly affected by either glycerol level or equilibration period, while after thawing, it was significantly higher (P<0.05) for 6.4 % glycerol and 5-h equilibrated semen than for 4 or 9 % glycerol and 1- or 3-h equilibrated semen, respectively. The PDA was lower with 4 % glycerol and 1-h equilibrated semen.     

野生与池塘、工厂化养殖牙鲆肌肉理化品质及质构特性比较研究

实验以牙鲆为研究对象, 测定野生与池塘、工厂化养殖牙鲆肌肉的持水性、胶原蛋白含量、肌纤维直径和质构特性, 以了解3种生长方式下牙鲆肌肉理化品质及质构特性的差异。结果表明: (1) 3种生长方式牙鲆有眼侧及无眼侧肌肉的滴水损失均呈野生组池塘组工厂化组(P0.01); 工厂化组失水率显著小于野生组及池塘组(P0.01), 而野生组与池塘组无显著差异(P0.05)。(2) 3种生长方式牙鲆有眼侧及无眼侧肌肉胶原蛋白含量和纤维直径差异均不显著 (P0.05)。(3)通过主成分分析, 发现黏附性和胶黏性是反映牙鲆肌肉质构特性的主要因素。工厂化养殖牙鲆肌肉具有较好的持水能力, 池塘养殖牙鲆肌肉的理化品质和质构特性与野生牙鲆相近。野生牙鲆并没有在理化特性上表现出明显优势。       

类囊体膜生物传感器的固定化研究

本实验以菠菜为材料 ,经过提取 ,用PUA SbQ、海藻酸钙和戊二醛—牛血清蛋白三种固定方法在 4 0孔板上固定得到固定化的类囊体膜 ,用酶标仪连续测定 8周固定化类囊体膜的光合活力变化。结果表明 :PVA SbQ固定方法最好 ,8周后测定的活性仍保持在 6 1 2 2 %左右。     

The effects of various diets on chitinase and ß-glucosidase activities and the condition of cod, Gadus morhua (L.)

Groups of cod, Gadus morhua (L.), were fed exclusively on fish, crustaceans, or crustacean shells for a period of 3 weeks. Chitinase and ß-glucosidase activities were measured in enzyme extracts of stomach contents, stomach tissue, pyloric caeca, intestinal contents, and intestine tissue, and compared to the enzyme activities of control fish starved over the same period. Fulton's condition factor K , liver lipid content and liver water content were determined to estimate the effects of the diets on the condition of cod.
general, the highest chitinase activities were measured in samples of cod that had been fed on whole crustaceans. In this feeding group, there was also a remarkable increase of activity by a factor of four to eight in the pyloric caeca, compared to the group fed on fish and the control group, respectively.
Measurements of ß-glucosidase activity revealed no similar dependence on food quality, ß-glucosidase occurrence seemed to be mainly restricted to the pyloric caeca and the intestine of cod.     

Influence of sugar supplementation of the extender on motility, viability and acrosomal integrity of dog spermatozoa during freezing

Influence of different sugars supplemented to the extender on the motility, viability and intact acrosome rates of dog spermatozoa during dilution, equilibration and freezing was studied. The ejaculate was divided into 10 aliquots, which were diluted 1:3 with TRIS-citric acid extender containing 240 mMTRIS, 63 mM citric acid, 8% (v/v) glycerol, 20% (v/v) egg yolk and 70 mM sugar, which was either fructose, galactose, glucose, xylose (monosaccharide), lactose, trehalose, maltose, sucrose (disaccharide) or raffinose (trisaccharide). No sugar was added to the extender in the control group. Extended semen samples were cooled to 5 degrees C over 45 min, packaged in 0.25-mL straws, equilibrated for 2 h at 5 degrees C and frozen in liquid nitrogen vapor. Samples were thawed by placing straws into 37 degrees C water for 30 sec. Motility, viable sperm and intact acrosome rates decreased gradually in all groups after equilibration and consecutively freezing (P<0.001). The type of sugar significantly effected motility, viability and acrosomal integrity during equilibration and freezing (P<0.05). Galactose, lactose, trehalose, maltose and sucrose reduced damaged acrosome percentages in equilibrated samples (P<0.05). Sugar supplementation did not enhance motility and viability during equilibration. The disaccharides, except lactose, reduced post-thaw dead sperm and/or damaged acrosome percentages without promoting post-thaw motility (P<0.01), whereas monosaccharides, especially fructose and xylose, improved motility (P<0.05) along with viability and intact acrosome rates (P<0.05). Trehalose, xylose and fructose significantly increased total active sperm rates (motility x live sperm rate x normal acrosome rate) compared to other sugars (P<0.01) and control (P<0.0001) in frozen thawed samples. Therefore, sugar supplementation of the extender influenced post-equilibration and post-thaw sperm quality, and the type or locality of protective impact of the sugar on dog spermatozoa vary according to type of the sugar.     

Interrelationships between Water and cellular metabolism in Artemia cysts. VIII Sorption isotherms and derived thermodynamic quantities

An analysis of water vapor sorption by cysts of the brine shrimp, Artemia salina, has shown that at environmental water activities (aw) of 0.95 or less, the cysts equilibrate with the aw of their environment. Above this aw the metabolic activity of the cysts participates directly in their water content, and equilibration does not occur. In contrast, dried cysts killed by heat treatment or exposure to ammonia fumes equilibrated with all values of aw examined. Analysis of the temperature dependence of sorption isotherms revealed that below cyst hydrations of about 0.3 g H2O/g dried weight the temperature coefficient for water sorption was negative, but became positive at hydrations appreciably in excess of this value. Estimates for the differential and integral net enthalpy and entropy changes accompanying the sorption of water have been calculated from isotherms. These results have been interpreted and integrated with those from previous work on the hydration-dependence of metabolic activity. All of the examined hydration properties of the cysts have been shown to be due chiefly to the cellular component, and not the acellular shell. Analysis of the data by the Bradley equation has shown that the hydration behavior of the shell obeys this relationship, whereas that of the cellular component does not.     

长江口中华绒螯蟹放流亲蟹对环境的生理适应

按回捕日期取样测定长江口中华绒螯蟹亲蟹标志放流前后血清与肝胰腺的生理指标, 初步研究了放流亲蟹对长江口环境的生理适应过程。结果表明, 在放流后6d, 亲蟹肝胰腺超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性以及血清甘油三酯(TG)和血蓝蛋白含量均降低, SOD、CAT和TG在放流后9d达到较低水平, 其中SOD活性和TG含量较放流前显著降低(P<0.05); 肝胰腺酸性磷酸酶(ACP)以及血清谷丙转氨酶(ALT)、谷草转氨酶(AST)、碱性磷酸酶(ALP)、总蛋白质(TP)、白蛋白(ALB)、总胆固醇(TC)和肌酐(CREA)水平在放流后总体呈现先升高后降低的趋势; 在放流后79d, 肝胰腺SOD、CAT、ACP与血清ALP、ALT、AST活性均恢复至放流前水平(P>0.05), 而血清TP、血蓝蛋白、ALB、TC、TG、CREA含量较放流前均显著降低(P<0.05)。综合各项指标表明, 中华绒螯蟹亲蟹在放流后6d内出现免疫力下降、代谢增强等反应, 放流22d后亲蟹各项机能逐步恢复, 并在70d后接近或达到放流前水平。建议今后放流前对亲蟹进行环境适应性驯化, 以便提高亲蟹增殖放流效果。     

The Maastricht Protocol for the Measurement of Body Composition and Energy Expenditure with Labeled Water

An update of practical aspects of the use of labeled water for the measurement of total body water (TBW) and energy expenditure (EE) is presented as applied in Maastricht, The Netherlands. We use a 10-hour equilibration period. The isotopes for the measurement of TBW and EE are routinely administered, after collecting a background urine sample, as a last consumption before the night. Our data show an underestimate of TBW measured with isotope dilution after 4 hours (in the morning), a discrepancy which increases with the size of TBW. No such relation and no significant differences were found after 10-hour (overnight) equilibration. The ratio between the dilution space for deuterium and oxygen-18 is higher than the earlier figure of 1.03, especially in adult subjects with a high body fat content. For an observation period of EE over two weeks, samples from the second and the last voiding on the first, mid, and last day of the observation period are collected. Differences in EE calculated from morning and evening samples within the first and second week allow detection of sampling errors and if so, samples are excluded from the final calculation. Differences of EE between weeks 1 and 2 allow a check for the consistency of the subjects' physical activity level and usually fall within 10% of the average EE over the total observation interval.     

Effects of equilibration time, precooling and developmental stage on the survival of mouse embryos cryopreserved by vitrification

Factorial experiments were carried out to examine the effects of equilibration time, precooling and developmental stage on the postthaw in vitro survival of vitrified mouse embryos. Eight-cell embryos, compacted morulae, or blastocysts were cryopreserved using vitrification Solution 1 (VS1; 10% glycerol + 20% propylene glycol), and vitrification Solution 2 (VS2; 25% glycerol + 25% propylene glycol) in phosphate buffered saline + 10% calf serum. Each embryo stage group was first equilibrated in VS1 for 5, 10 or 20 min and then exposed to either a precooled ( approximately 4 degrees C) or nonprecooled ( approximately 20 degrees C) VS2 in a 0.25-ml straw before they were plunged directly into liquid nitrogen. Results of this study showed an interaction between precooling, equilibration time and developmental stage which affect significantly post-thaw embryo survival (P< 0.05). High survival rates were obtained after 10 min equilibration in VS1 irrespective of the embryo developmental stage. Precooling of the VS2 significantly improved the survival mainly of blastocysts. However, eight-cell and morula-stage embryos also showed high survival rates when they were exposed to precooled VS2 after 5 min equilibration in VS1. It was further observed that morulae usually exhibit high survival rates, and vitrification conditions are more critical for early and advanced stage embryo development.     

Role of equilibration before rapid freezing of mouse embryos

The time requirements for permeation by glycerol and dehydration by sucrose before rapid freezing of Day-3 mouse embryos by direct transfer to -180 degrees C were studied. When the embryos were equilibrated in 2.0, 3.0, or 4.0 M-glycerol + 0.25 M-sucrose for 2.5 to 40 min, the post-thaw viability increased (P less than 0.001) with the length of equilibration period at 4 degrees C. At 20 degrees C the volume of embryos increased with the duration of equilibration up to 20 min (P less than 0.001), but the post-thaw viability was not affected. The effect of equilibration in glycerol-sucrose was determined at 20 degrees C for embryos which were previously permeated by glycerol, dehydrated by sucrose or left in PBS + 5% FCS. The survival of previously permeated embryos was not affected by equilibration for 1-16 min in glycerol-sucrose. The maximum survival rate was attained after shorter equilibration in glycerol-sucrose for embryos without pretreatment (4 min) than for those previously dehydrated (8 min). It is concluded that increases in the intracellular glycerol level are beneficial for the viability of rapidly frozen mouse embryos and previous or concomitant exposure to sucrose unfavourably affects glycerol permeation.     

云南典型热带森林生态系统中微量元素的生物地球化学特征研究

本文以我国云南典型热带森林生态系统为研究对象,在物质循环较封闭的地段,按照不同地貌部位、不同的物质淋溶堆积景观类型进行采样,采样时在同一单元景观内同时收集土壤、风化壳、植物和天然水的样品,分析各样品中九种重金属元素的含量分布以及土壤风化壳样品中各元素的六种赋存形态的含量分布,通过对比元素在不同单元景观间、不同景观要素间和景观要素内部的分异特征,从而给出热带森林生态系统中元素的分布形成规律和动态分异特征。     

灭幼脲Ⅰ号对致倦库蚊幼虫磷酸酶活力的影响

本文用稍加改良的磷酸苯二钠法,测定了经灭幼脲Ⅰ号处理的致倦库蚊4龄期幼虫的酸性磷酸酶(ACP)和碱性磷酸酶(AKP)活力的变化,发现被处理幼虫的这两种磷酸酶活力均受到影响。在整个4龄期,灭幼脲Ⅰ号对AKP活力的抑制都比较明显,抑制强度甚至达80％,对ACP活力的抑制则比较弱;但在化蛹前,当对照幼虫的ACP活力增高时,被处理幼虫的ACP活力却下降,致使两者活力也相差一倍以上。由于灭幼脲Ⅰ号对幼虫两种磷酸酶产生明显的抑制作用,从而导致幼虫的生长发育缓慢,幼虫4龄期延长,幼虫不能化蛹而终于死亡。     

EFFECT OF UNILATERAL VISUAL DEPRIVATION AND VISUAL STIMULATION ON THE ACTIVITIES OF GLUTAMATE DECARBOXYLASE, GABA-α KETOGLUTARATE TRANSAMINASE, ASPARTATE AMINOTRANSFERASE AND HEXOKINASE OF THE OPTIC LOBE OF THE ADULT PIGEON

Abstract— A study was made of the effect of unilateral visual deprivation and stimulation upon the activities of glutamate decarboxylase (EC 4.1.1.15), GABA-α-ketoglutarate transaminase (EC 2.6.1.19). aspartate aminotransferase (EC 2.6.1.1) and hexokinase (EC 2.7.1.1) in the optic lobe of the adult pigeon ( Columba Livia ). Visual deprivation was achieved by eyelid suturing or by enucleation and maintained for 1–9 weeks. Unilateral visual stimulation was maintained for 75 min following 72 h in the dark. A small but significant increase was observed in the activities of glutamate decarboxylase and aspartate aminotransferase after unilateral visual stimulation and a decrease after unilateral enucleation. The activities of GABA-α-ketoglutarate transaminase and hexokinase decreased after unilateral visual stimulation and increased after enucleation. Unilateral eyelid suturing resulted in a significant reduction in the activity of glutamate decarboxylase and an increase in the activity of GABA-α-ketoglu-tarate transaminase. Hexokinase activity was, however, unchanged following unilateral eyelid suturing.     

Glass transition temperatures of cassava starch-whey protein concentrate systems at low and intermediate water content

Glass transition temperatures of cassava starch (CS)-whey protein concentrate (WPC) blends were determined by means of differential scanning calorimetry (DSC) in a water content range of 8-20% (dry basis, d.b.). Water equilibration in the samples was carried out by storing them at room temperature (25 °C) during four weeks. Physical aging and phase segregation were observed in some samples after this storage period depending on the water content. Both, first DSC heating scans and tan δ curves of CS-WPC blends with intermediate water content (10-18%), showed two endothermic thermal events. The first one appeared at around 60 °C and was independent of water content. The second one was detected at higher temperatures and moved towards the low-temperature peak as the water content increased. The results can be explained by a phase segregation process that can take place when the samples are conditioned below their glass transition temperatures. The Gordon-Taylor equation described well the plasticizing effect of water on the blends. WPC was also found to decrease the glass transition temperature, at constant water content, an effect attributed to additional water produced during browning reactions in the blends.     

盐度对花鳗鲡和太平洋双色鳗鲡幼鳗生长性能及消化酶活力的影响

文章研究了不同盐度对花鳗鲡(Anguilla marmorata)幼鳗和太平洋双色鳗鲡(A. bicolor pacifica)幼鳗生长性能及消化酶活力的影响。将花鳗鲡幼鳗(9.760.36) g和太平洋双色鳗鲡幼鳗(11.820.04) g分别在淡水(盐度0)与盐度5、10、18水体中养殖30d, 测量每组实验鱼总重后检测胃、肠道和肝脏蛋白酶、淀粉酶和脂肪酶的活力。结果表明, 花鳗鲡和太平洋双色鳗鲡在各盐度处理中存活率均为100%, 未出现死亡。两种鳗鲡在淡水中生长良好, 特定生长率最高, 而饵料系数最低。盐度对花鳗鲡幼鳗和太平洋双色鳗鲡幼鳗消化酶活力的影响存在差异, 其中花鳗鲡胃、肠道和肝脏蛋白酶活力在各盐度处理中均无显著变化(P0.05), 淀粉酶和脂肪酶活力均随盐度的增加而下降; 太平洋双色鳗鲡胃蛋白酶活力在盐度10时最大, 肝蛋白酶活力在盐度18时最大, 而淀粉酶和脂肪酶活力在各盐度处理组无显著变化(P0.05)。这表明盐度对花鳗鲡胃、肠道和肝脏的淀粉酶和脂肪酶活力具有抑制作用, 对太平洋双色鳗鲡的蛋白酶活力有一定的激活作用。在相同盐度条件下, 不同消化器官中同种消化酶活力存在差异, 各盐度的两种鳗鲡肠道中淀粉酶和脂肪酶的活力均显著高于肝脏和胃(P0.05), 胃中蛋白酶活力高于肝脏和肠道, 但不显著(P0.05)。研究发现两种鳗鲡体内脂肪酶活力相对较高, 表明其对脂肪具有较强的消化能力。建议在配制花鳗鲡幼鳗和太平洋双色鳗鲡幼鳗饲料时, 适当提高粗脂肪比例, 有助于促进对营养物质的消化吸收, 提高养殖效益。       

The Action of Pitressin on Solute Permeability of the Rabbit Nephron in Vivo

The isotopic equilibration of urea, thiourea, and inulin between urine and plasma was determined in rabbits in the presence or absence of antidiuretic hormone (ADH). Animals were anesthetized with ethanol and permitted to reach steady state after completion of surgery. Tracer was then administered by intraarterial infusion in such a manner that a high constant specific activity in plasma was rapidly attained. Urine flow was kept independent of ADH by addition of mannitol. Urea/creatinine clearance ratios and the accumulation of urea in renal medulla and papilla also remained unaffected by ADH. Under these conditions, thiourea and inulin at all times approached equilibrium, at similar rates. In the absence of ADH, urea also equilibrated at a rate similar to that of inulin. The addition of ADH, however, significantly prolonged the delay before urinary urea reached the high constant specific activity of plasma urea. These observations are interpreted in terms of a specific effect of the hormone on the solute permeability of the nephron.     

Sperm cryopreservation of a live-bearing fish, the platyfish Xiphophorus couchianus

The objectives of this study were to evaluate the effects of cryoprotectant, osmotic pressure, cooling rate, equilibration time, and sperm-to-extender ratio, as well as somatic relationships of body length, body weight, and testis weight to sperm density in the platyfish Xiphophorus couchianus. Sperm motility and survival duration after thawing were significantly different between cryopreservation with dimethyl sulfoxide (DMSO) and glycerol, with the highest motility at 10 min after thawing obtained with 14% glycerol. With subsequent use of 14% glycerol as cryoprotectant, the highest motility after thawing was observed with Hanks' balanced salt solution (HBSS) across a range of 240-300 mOsm/kg. Samples cooled from 5 to -80 degrees C at 25 degrees C/min yielded the highest post-thaw motility, although no significant difference was found for cooling rates across the range of 20-30 degrees C/min. In addition, the highest motility after thawing was found in samples equilibrated from 10 to 30 min with 14% glycerol and cooled at 25 degrees C/min. The post-thaw motility declined rapidly with use of 10% glycerol and cooling at 5 degrees C/min across the equilibration range of 10 min to 2h. Sperm motility with a dilution ratio of sperm to extender of 1:10 was not different at 10 min after thawing with those samples at greater dilutions, but declined significantly from Day 1 after thawing and showed lower survival duration when stored at 4 degrees C. However, the additional dilution of sperm solutions with HBSS (300 mOsm/kg) immediately after thawing significantly slowed the decline of motility and prolonged the duration of survival. Based on the above findings, the highest average sperm motility (78+/-3 %) at 10 min after thawing was obtained when sperm were suspended in HBSS at 300 mOsm/kg with 14% glycerol as cryoprotectant, diluted at a ratio of sperm to HBSS-glycerol of 1:20, equilibrated for 10 min, cooled at 25 degrees C/min from 5 to -80 degrees C before plunging into liquid nitrogen, and thawed at 40 degrees C in a water bath for 7 s. If diluted within 5 h after thawing, sperm frozen by the above protocol retained continuous motility for 15 days when stored at 4 degrees C.     

THE REGIONAL AND SUBCELLULAR DISTRIBUTION OF CATECHOL-O-METHYL TRANSFERASE IN THE RAT BRAIN

Catechol-O-methyl transferase (COMT) activities determined in different regions of rat brain showed small variations. Highest activities were found in the hypothalamus and corpora quadrigemina, and lowest activities in the hippocampus and corpus striatum. The regional distribution of COMT was thus at variance with the distribution of DOPA decar- boxylase in this study and with the distribution of catecholamines and tyrosine hydroxylase reported in the literature. Determinations of the subcellular distribution of COMT in rat forebrain showed that 50 per cent of the activity was recovered in the high speed supernatant fluid and about 33 per cent in the crude mitochondrial fraction. Further separation of the latter by discontinuous sucrose gradients showed that the particulate COMT was found in the synaptosomal fraction in an occluded form. Full enzyme activity was only obtained after treatment with a detergent or after resuspension in water. After hypo-osmotic rupture of the crude mitochondrial fraction, COMT was recovered in the cytoplasmic fraction. The subcellular distribution of COMT was very similar to the ones of lactate dehydrogenase and DOPA decarboxylase. The proportions of soluble COMT obtained from homogenates of various regions of the brain differed from that of choline acetyl transferase and DOPA decarboxylase but were similar to that of lactate dehydrogenase. In conclusion, COMT is a cytoplasmic enzyme almost evenly distributed in the CNS. Its distribution does not resemble the distributions of the catecholamines or of the enzymes participating in the synthesis of catecholamines.     

EFFECT OF SOIL MOISTURE STRESS ON THE CORRELATION BETWEEN HEAT PULSE VELOCITY AND TRANSPIRATION

(1) Heat pulse velocity in the stem of pine and sour orangeseedling, measured by HUBER's heat pulse method, was correlatedwith transpiration as measured by determining the humidity ofair passed over the plant. This correlation was used to calculatetranspiration under natural conditions, when heat pulse velocityonly was measured. (2) It was shown that heat pulse velocity at a given transpirationrate was related to water stress. When water potential in thesoil decreased heat pulse velocity increased in pine seedlingsand decreased in sour orange. This effect of water stress didnot appear to be completely reversible. Under conditions ofvery low water potential in the soil, no useful correlationbetween transpiration and heat pulse velocity could be obtainedeither in pine or sour orange. (3) From the data obtained it is concluded that transpirationcan be reliably calculated from heat pulse velocity measurementsonly if the calibration curve relating transpiration to heatpulse velocity is determined shortly beforehand under similarconditions of soil moisture and potential evapotranspiration.Even so, only total daily transpiration can be estimated bythis method. Hourly figures of transpiration are unreliable,especially under conditions conducive to low water potentialin the plant. (Received June 24, 1964; )