February 26, 1898, 



GARDENERS 



MAGAZINE. 



133 



before us that we must just point out that in the case of an action like denitrifica- 

 tion, requiring the concurrence of several condition?, each of them equally 

 essential, the activity of this action in any particular case cannot be taken as proof 

 of a special preponderance of one of these conditions, but rather as showing that 

 all are fully present. 



There is, however, one reason which would lead us to expect that animal 

 excrement would contain a relative abundance of the dentrifying organism. If 

 we may assume, as we probably may, that the denitrifying bacteria present in the 

 food pass uninjured through the intestin s, it is evident that they will occur in 

 larger proportion in the solid excrement than in the original food. If, for instance, 

 a horse is fed on hay, and digests one-half of the food consumed, the dung will 

 then contain twice the proportion of the denitrifying bacteria originally present in 

 the food. The proportion of the organisms supplied by different kinds of food 

 must vary greatly. If the bacteria are, as we assume, deposited from the 

 atmosphere, and lie in all cases on the surface of the food, their proportion must 

 depend largely on the extent and character of the surface, and on the length of 

 exposure to the atmosphere. A hundred pounds of hay should contain a far 

 greater proportion of bacteria than a hundred pounds of green mangel or turnips. 

 From this point of view there is thus some ground for assuming that horse excre- 

 ment will be richer in denitrifying organisms than cattle excrement. 



Before further discussing the question before us we must, observes Profeszor 

 Warrington, turn once more to the results of former investigations, and see what 

 are the precise conditions necessary to induce denitrification. 



Schloesing (1873), in his investigation on the rate of nitrification in soil, kept 

 various portions of the same moist, humous soil, in atmospheres in which different 

 proportions of oxygen were constantly maintained throughout the experiment. He 

 found that the quantity of nitrate produced in the soil steadily diminished as the 

 proportion of oxygen in the air decreased ; when, however, no oxygen was present, 

 denitrification took place, and the nitrates originally contained in the soil entirely 

 disappeared. He repeated the experiment, this time adding a known amount of 

 saltpetre to the soil. He found that such a soil, placed in a vessel containing 

 very little air, first absorbed all the oxygen present, and then evolved a consider- 

 able quantity of gas ; this gas contained nitrogen equivalent to the whole of that 

 contained in the saltpetre added. The consumption of the oxygen of the air had 

 thus determined denitrification. 



^ The supply of atmospheric oxygen to a soil is effectually prevented if the soil 

 is kept saturated with water ; this condition alone is sufficient to set up an energetic 

 denitrification. In an experiment made by Professor Warrington in the Rotham- 

 sted laboratory in 1880, and published in the R.A.S. journal in 1881 (p. 332), 

 seven pounds of dry, finely-powdered loam were places in a percolator, and 

 thoroughly saturated with water ; the column was about eight inches deep. The 

 nitrates naturally present having been entirely removed by the passage of water 

 through the soil, a known quantity of nitrate of sodium was placed on the sur- 

 face. Alter a week had elapsed a small quantity of water was placed each day 

 on the surface of the soil, and the drainage water removed and analysed. When 

 nitrates no longer appeared in the drainage water it was found that only twenty-one 

 per cent, of the nitrate applied to the soil had been recovered ; seventy-nine per 

 cent, had been lost. The mode in which this loss had occurred was evident to 

 the eye ; the column of soil, though always kept in a saturated condition, was cut 

 across about the middle with Urge transverse fissures, the result of the formation 

 of gas within the soil. In another experiment, made with the same soil under 

 identical conditions, in which an equivalent quantity of chloride of sodium was 

 employed, the whole of the salt applied was recovered in the drainage water, and 

 no fissures appeared in the column of soil. 



A recently-published experiment by Breal furnishes a further excellent example 

 ot the active denitrification which takes place in a soil kept saturated with water. 

 He placed some garden soil in a percolator and consolidated it by pressure ; the 

 column was about fifteen inches high. Water, more than sufficient for saturation, 

 was then poured upon the soil. When the water had run through it was poured 

 back again over the soil, and this treatment was continued for some time. The 

 soil at the commencement of the experiment was in an active state of nitrification, 

 ?nd the drainage water was at first rich in nitrates, but at the end of three weeks 

 trie nitrate had entirely disappeared from the drainage water, though no water had 

 been removed from the soil. 



We have now the conditions which bring about a loss of nitrogen by denitrifica- 

 tion p'amly before us. There are needed : 1. The specific organism. 2. The 

 presence of a nitrate and suitable organic matter. 3. Such a condition as to 

 aeration that the supply of atmospheric oxygen shall not be in excess relatively to 

 me supply of organic matter. 4. The usual essential conditions of bacterial growth, 



Work 



the Week. 



as plant food, and a suitable temperature. ' 



Of these conditions, the supply of organic matter is by far the most important 

 in determining the extent to which denitrification will take place. An abundance 

 ot the special organism is of comparatively little importance ; for, if the conditions 



r, ?f u u rabIe for its S rowth and development, it will increase with such 

 rapioity that the number of organisms originally present will soon become a matter 

 or indifference. Nothing, however, will compensate for a deficiency of organic 

 matter ; rf this is small in quantity, the action will be strictly limited in extent, 



nrin^T /I 6 may - be the su PP J y of the s P ecific nanism. This fundamental 

 ffr ot tn « taction has been strangely overlooked by the German investigators 

 wnen interpreting the results of their experiments. They have sought to explain 

 .l,""' 1 inca .t'on m their experiments as due to the supply of additional organ- 



„, ? e soU m the form of manure, when the results were really due to the 

 supply of an excess of organic matter. 



nnanWf Gay ° n , and Dupetit's investigations the preponderating influence of the 

 IKS • or ganic matter present is fully recognised. The same organism 



£™ J -f Wage and in chicken brolh > reduced in the first instance cri to 0 2. 

 exoTriLnt C htre ' and in the second instance fift y grams per litre. Some 

 diluted nrTn my °, wn are eo < ual, y cIear nn the P° im - Tw o equal volumes of 

 the Mother T ^ take ? ; one received nitre at the rate of gram per litre ; 

 Both snlnti™ nitre and su g ar » each at lhe rate of five grams per litre, 



solutions £° eiVed °' 5 gram of Soil t0 SU P p,y the deni 'trifying organism. The 

 intS t 7! re ? en c f ° Vered with a layer of paraffin oil to exclude air, and thus 

 decrees V h ° r the or g anic matter, and were kept at a temperature of 70 

 occurred ? a • the s o ,u tion containing no sugar a slight evolution of gas 

 Phce Th " te l a PPeared in the liquid ; some reduction of nitrate thus took 

 in the solnt? °? u sto P Ded . and much of the nitrate remained permanently 

 Dresenr ~ . the sec <>nd case, in which five times the quantity of nitre was 



a D D«ir«l a f com Panied by its own weight of sugar, the whole of the nitrate dis- 



deerminJ V " days ' The presence or absence of sugar thus entirely 

 e.ermmed the extent to which denitrification would take place 



contiirW Dr^c^^ir? t0 the S ar(ien for the whole year is the "Gardening Ye 



"Gardenir ^M^n^Ss ° D th ? cu,tiva «° n of Flowers, Fruit, Vegetables, &c. 



5 ^saane Office, 4, Ave Maria Lane, London.— [Ad vt.] 



WARM ORCHIDS. 



The days are now lengthening, and the occasional sunshine reminds us of the 

 vast amount of important work to be done. In almost every house there are some 

 plants needing especial and immediate attention. Some require repotting, others 

 top-dressing, &c, and if the summit of success is to be reached then the necessary 

 assistance must be rendered. If a good stock of the best orchid peat has not 

 been obtained, it is quite essential to purchase such forthwith, and also a good 

 stock of teak baskets in different sizes and shapes in order to suit requirements. 

 The pot-shaped baskets are used a great deal, and, generally speaking, are the 

 best. Dendrobiums and cattleyas thrive well in them, as their long roots have 

 something to cling to for a longer period than in the square ones. Phakenopsis will 

 require a slight shading for a short time in the day when the sunshine is rather strong, 

 otherwise they are bound to flag, and the temperature will rise too quickly and 

 fall in a similar way when the sun goes down ; it is therefore very important that 

 this point be considered, for spot appears largely as the result of fluctuations of 

 temperature. A slight damping in the afternoon will be required as well as in 

 the morning, balanced with a free circulation of air night and day, wind and 

 weather permitting, the bottom ventilators being left open on the reverse side to 

 the wind, and both sides when fit. Dendrobiums that were removed to a warmer 

 house to flower will now be starting into growth ; repotting or rebasketing must 

 be done at once, and after this place the specimens in about 62 degrees of heat 

 for a start, and the watering must be done very cautiously ; a slight occasional 

 syringing is very beneficial. Let the stock still resting be examined, and all that are 

 showing signs of growth or that have buds (unless some are being retarded) should 

 be removed to a warmer house— five degrees warmer — in order to start them 

 quietly and bring on the flowers gradually. Young seedlings must be repotted also 

 at this season. 



Cattleya labiata autumnalis must now be repotted or top-dressed as required ; 

 those that require repotting must be shaken from the old material, and, so as not to 

 injure the roots that cling round the outside of the pot, the pot must be broken ; 

 arrange the roots close to the fresh pot, to enable them to have full benefit of the 

 humid atmosphere, at the same time arranging the lead of the plant as near the 

 middle as possible. Crock the pots three parts full and use good fibrous peat, 

 after shaking out all the dust, mixing it with clean green sphagnum, trimming all 

 off nicely with a pair of scissors. Cattleya Triana?, having passed out of flower, 

 must be served likewise. Cattleya Bowringiana that was not potted earlier must 

 receive immediate attention, taking care that the plants are kept well up in the 

 pot, as they make their growths low down. Angnecum that have finished 

 flowering must also be attended to. Cymbidium Lowianum and its hybrids will 

 now be growing fast and also producing strong spikes, so plenty of water will 

 be needed, and a dose of weak liquid cow-manure will help the flowers, giving 

 them vigour and bringing out the colour ; Cymbidium eburneum will require the 

 same care. Lselia anceps are now rooting freely, and a slight syringing among 

 the baskets will encourage these. Fumigating must be done on quiet days, and a 

 keen eye must be kept for scale, using brush or sponge to eradicate it before it 

 becomes established. The phakenopsis house should register 65 degrees by night 

 and 70 degrees by day ; cattleya house, 60 degrees by night and 65 degrees by day ; 

 intermediate house, 58 degrees by night and 62 degrees by day. — T. Stafford, 

 Tyntesfield Gardens. 



STOVE PLANTS. 



In our stoves the majority of plants will have commenced growth, and 

 if not already done, the necessary repotting should be attended to at once before 

 the sun gains too much power, else flagging and loss of many leaves will be the 

 result. After repotting, watering requires to be done with great care ; the fewer 

 applications of water possible, consistent with the welfare of the plant, until the 

 roots are working freely in the new soil, the better. One hears many complaints 

 about the nature of the soil used in many gardens not being suitable for the growth 

 of plants in pots — in many such cases the fault can easily be traced to injudicious 

 use of the watering pot directly after potting — thus souring the soil before it is 

 occupied by active-feeding roots. Large shifts are to be avoided, unless the one 

 in charge can be relied upon to use the water-pot with discretion, else disaster is 

 sure to ensue. Beware of dribblets, which only moisten the surface soil and never 



Lr Book,' 



Price is, 



penetrate to the lower stratum. In all cases of newly-potted plants defer watering 

 as long as possible, and when it is applied, give sufficient to moisten every particle 

 of soil in the pot. Syringe freely amongst the pots, damp floors and walls, and 

 afford as little air as possible, as by such treatment plants will soon recover them- 

 selves, and suffer very little check from the process of repotting. Gloxinias which 

 were started in January should be now well established in five or six inch pots, 

 and showing their flowers ; keep them in a light position, and standing on a moist 

 base if possible, they like plenty of moisture in the air, but are better if not 

 syringed overhead ; give them an occasional sprinkling of patent manure, they 

 are also partial to an occasional application of soot water, not too strong. Start 

 batches fortnightly, potting them on as required ; we use a compost of two parts 

 loam, one part leaf-soil, half a pa t of cocoanut-fibre refuse and sand, in the case 

 of older tubers a little decayed manure is incorporated. Prick off seedlings of 

 gloxinias as soon as large enough to handle, mixing plenty of leaf-soil and sand in 

 the medium into which they are pricked out. Seedlings of Isolepis gracilis, 

 Cyperus alternifolius, eulalias, &c, are better potted two or three together into 

 thumb pots. If seed is sown now of Panicum plicatum, useful plants for furnish- 

 ing will be produced by the early autumn ; this is a very useful subject for many 

 purposes, not the least being the utility of its foliage for mixing with flowers in 

 large vases in the rooms ; it is often mistaken for a slender-growing palm. 



Alocasia Lowi, A. Veitchi, and A. metallica are plants of noble foliage, and 

 are striking objects either as permanent occupants of the stove, or for exhibition 

 and furnishing purposes. In potting these avoid soils of an adhesive nature, use a 

 compost of peat, chopped sphagnum, sand, and charcoal ; the drainage must be 

 thorough, as when growing they require an abundance of water. Aiocasia 

 macrorhiza variegata may be potted in a compost consisting of two parts loam, one 

 part leaf-soil, a little decayed manure, and a good admixture of sand. Justicia 

 carnea, and J. c. rosea are very old occupants of our stoves, and perhaps it i* on 

 that account they are so very seldom seen now ; at any rate, wherever they are 

 grown they are appreciated. They can be had in flower over the greater part of 

 the year by inserting cuttings at different times. They will root freely in a tempeia- 

 ture of 65 degrees, with or without bottom heat ; insert the cuttings singly in two- 

 and-a half-inch pots, shade from bright sun, and give a sprinkle overhead now and 

 again during the day ; when rooted shift into six-inch pots, in which they will 

 flower, using for a compost three parts loam, one part leaf-soil, and one half part 

 old mushroom-bed manure with sand added ; they are partial to a free use of the 

 syringe. Anthurium Scherzerianum, A. Andreanum, and other kinds, with their 

 quaint flowers, and more or less brilliant colours, are worthy of space in even the 

 smallest stove* During the growing season they delight in copious supplies of 



