In maize (Zea mays L.) grown under normal conditions in Rhodesia, prevention of pollination or removal of the ears after flowering caused premature senescence of the leaves above the ear, preceded by the appearance of a purplish red color. In plants from which the ears had been removed the concentration of sugars and starch increased markedly in both upper and lower leaves, the increase being greater in the upper leaves.The removal of flowers or of developing fruits has been observed to delay senescence in a number of annual plants (5). In contrast, we have noticed in Rhodesia that the removal of developing ears causes leaves of maize plants to wither prematurely. Two experiments were conducted to investigate this problem. METHODSIn both experiments the locally bred single-cross hybrid 59H17, known commercially as SR52, was grown under normal conditions on fertile soil at a density of 31,000 plants per hectare (12, 500 plants per acre).In the first experiment, we investigated the effect of ear removal or prevention of pollination on leaf senescence. There were four treatments, viz., a control, ear removal 13 or 27 days after silk emergence, and covering the silks during the period of pollen shedding. Plots consisted of 10 plants in four replicates.At the time of flowering the area of every leaf was measured on 20 plants. Subsequently, the green, i.e., unwithered, leaf areas were estimated at weekly intervals until 8 weeks after flowering, and the green leaf area above and below the ear was calculated (1).In the second experiment we studied the effect of ear removal on carbohydrate accumulation. This experiment consisted of two treatments in three replicates, namely, a control and ear removal 19 days after flowering.Samples of leaf laminae were harvested from both above and below the ear on three occasions, namely, 7, 17, and 28 days after ear removal. Each sample consisted of 10 laminae, obtained by collecting either the middle two of the laminae above the ear, or the middle two of the laminae below the ear from each of five plants. Parts of some laminae had withered by the time of the third harvest, and these parts were discarded.The samples were always collected shortly before noon and within half an hour were placed in a forced draught oven at a temperature of 110 to 120 C for 20 min and then dried for about 6 hr at 60 to 70 C.The dried samples were finely ground and analyzed for total nonstructural carbohydrates with Clarase 300 (9). Since fructosans do not occur in maize (2), the results represent total sugars plus starch, expressed as glucose. In addition, reducing and nonreducing sugars were determined after extraction with alcohol (8); the replicate samples for the third harvest were analyzed separately, but for the first two harvests composite samples from the three replicates were used for the sugar determinations. Starch was calculated by difference: (total nonstructural carbohydrates minus total sugars) x 0.9. All analytical results are expressed as percentages of the dry matter. RESULTSExper...
The roots of plants are the least known, least understood and least appreciated part of the plant."-^\Veaver and Bruner (125).The underground parts of perennial grasses serve not only as anchorage and organs of absorption of water and nutrients, but also for the storage of reserves, and there exist significant interrelations between herbage growth and underground development. The aim of modem grassland husbandry is to produce and maintain maximum yields of high qiiality fodder. To achieve this, an imderstanding of the functions of the undergromid organs, their relations to the aerial parts, and their responses to environmental factors and cultviral treatments appears indispensable. Our knowledge on this subject is still fragmentary, and it is hoped that this reView of available evidence will stimulate further research on these matters. SEASONAL UNDERGROUND DEVELOPMENTOnly a limited amount of work has been undertaken regarding the seasonal development of the roots and other underground organs of grasses. According to Trowbridge and co-workers (1) the weight of the corms of Phleum pratense, growing under Missouri conditions, was lowest in spring, and increased rapidly to the early bloom stage and then more slowly to maturity. Brown (2), also working in Missouri, found that spring and autumn were the more favourable seasons for root and rhizome growth in Poa pratensis. Root growth was most active during early spring at mean temperatures below 60°F, whereas rhizomes developed most rapidly in late spring and early summer. Both roots and rhizomes usually lost weight during summer at mean temperatures near or above 80°F.In Germany, Remy (3) obtained evidence that in Dactylis glomerata, grown in the greenhouse, the weight of the root system increased from mid-summer to late autumn. The seasonal root development of the same species was studied at Aberystwyth by Stapledon and Milton (4), who found that in plants grown in the open, root development was progressive from April to September. Sturkie (5) found that the root-stocks of Sorghum halepense developed after the aerial parts had matured, and according to Sampson and McCarty (6), root growth in Stipa pulchra occurred in autumn and winter when herbage growth had practically ceased, SimUar observations were made by Weinmann (7) on Chloris gayanq,, Rhodes grass. 115
IntroductionThe estimation of sugars is a matter of interest to every worker engaged in the study of carbohydrate metabolism and related problems. In order to be of any real value a method must not only allow the determination of relatively small amounts of sugars with sufficient accuracy, but should also be rapid, and thus permit of a large number of determinations being carried out in a short time. Semi-micro modifications of the Munson-WalkerBertrand method (1, 5) have been elaborated by ILJIN (2) and WILDMAN and HANSEN (7) with the object of satisfying these demands as nearly as possible. The method of WILDMAN and HANSEN unfortunately requires apparatus which is not available in every laboratory. ILJIN'S modification attracted the writer's attention on account of its simplicity.In ILJIN'S method centrifuge tubes containing 6-ml. aliquots of the sugar solution and 6 ml. of Fehling's solution (of a higher concentration than used in the original Munson-Walker method) are heated in a boiling water-bath for ten minutes. After cooling, the precipitate is separated from the liquid by centrifuging, washed, and dissolved in acid ferric ammonium sulphate solution. The latter is then titrated with potassium permanganate solution.
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