UNIVERSITY OF CALIFORNIA PUBLICATIONS IN AGRICULTURAL SCIENCES Vol. 1 , No. 11 , pp. 34 1 -394, plates 5- 1 5 January 31, 1917 [NFLUENCE OF THE COMPOSITION AND CONCENTRATION OF THE NUTRIENT SOLUTION ON PLANTS GROWN IN SAND CULTURES BY ARTHUR HUGO AYRES INTRODUCTION Since the recognition of the fact that the mineral content of the plant body is derived from the mineral constituents of the soil, the part which the soil solution takes in the nutrition of the plant has been the subject of numerous investigations by chemists, plant physiologists, and soil scientists, who have made large contri- butions to our knowledge in this important field. The early investigations of Knop and other plant physiologists showed conclusively that the elements which are essential to plant growth are carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, potassium, magnesium, calcium, and iron. As most of this work was done before the development of the new chemical and physi- cal theories, in regard to solutions in particular, the problems dealing with the absorption of these elements remain for expla- nation in the light of this new knowledge. The modern period of research in this field has thus been characterized by an in- tensive study of the absorption of nutrient elements by the plant. The earlier conceptions, which had a marked tendency to link each element with some specific physiological process or with the development of some morphological part of the plant, have been 342 University of California Publications in Agricultural Sciences [Vol. 1 largely discarded in view of the recent investigations, which have shown that plant growth is not a simple function of any any particular element, but is to a very large extent influenced by the combinations of elements in the solution from which the plant derives its nourishment. Thus while calcium may in certain cases act as a neutralizer of oxalic acid,1 it exhibits a more general function of antagonism for salts of potassium, sodium, magnesium, and other salts which would be toxic if calcium were not present.2 While this antagonistic function may be characteristic, it would seem from the experiments of Tottingham3 that either this antagonistic action of calcium or the toxic effects of magnesium are influenced by the total con- centration of the solution. Tottingham, therefore, concludes that the injurious effects of magnesium depend not only on the amount of calcium present but also upon the complex balance between all the salts in the solution. It follows that while the later in- vestigations have undoubtedly given a wider conception of the role of the various nutrient elements, the exact relation which exists between the recognized nutrient function of these elements and the balancing function in the solution is not definitely known. The part which the total concentration of the solution takes in the complicated problem of plant nutrition is by no means clear. On the one hand, the experimental evidence of Cameron4 and his co-workers shows that the plant growing in water culture is not influenced to any extent by wide variations in the total concentration of the solution, a view which is further supported by the researches of Tottingham,5 who concludes that nutrient solutions ranging from 0.01 per cent to 0.14 per cent do not affect the dry weight in the case of wheat grown in these solutions. A similar view is taken by Stiles," who thinks that the individual variation of plants grown in water cultures is as large or larger than that which is often accredited to a variation in the compo- i Schimper, Flora, vol. 73, pp. 207-261, 1890. 2 Loew, Flora, vol. 75, pp. 368-394, 1892; and U. S. Dept. Agric. Bur. Plant Ind. Bull. 45, 1903; Osterhout, Bot. Gaz., vol. 42, pp. 127-134, 1906, and vol. 44, pp. 259-272, 1907. s Tottingham, Physiol. Res., vol. 1, pp. 133-245, 1914. * Cameron, Jour. Phys. Chem., vol. 14, p. 320, 1910. s Loc. cit. o Stiles, Ann. Bot., vol. 29, pp. 89-96, 1915. 1!H7| Ayres: Nutrient Solution on Plants Grown in Sand Cultures 343 sition of the solution. In decided contrasl to 1 1 1 « - evidence cited above, we have the investigations of Hall, Brenchley, and Under- wood,7 who eonelnde, on the basis of their results with barley plants grown in a standard solution of four different concen- trations, thai "the growth made by plants in the soil solution is in the main determined by the amount of plant food they con- tain," and that "the concentration of the nutrient solution within certain wide limits, irrespective of the total amount of the plant food available, is a factor in the rate of plant growth which varies directly though not proportionally with the strength of the solution in the particular mitrienl or nutrients limiting the growth.** The experiments of Shive8 are of considerable interest in this connection. "Wheat was grown in solutions of three different total concentrations, 0.1, 1.75, and 4.00 atmos- pheres, in terms of possible osmotic pressure. The solution used was the three-salt solution first used by Birner and Lucanus9 ► containing Ca(NO.,)2, MgS04, and KrLP04. All possible sets of proportion of these salts were included for increments of change equal to one-tenth of the total possible osmotic pressure. As judged from the extensive quantitative data collected, Shive concludes that the growth of wheat plants in solutions of any given salt proportion is determined by the concentration of the medium. In the course of some experimental work concerning the drop- ping of flowers by b\ species-hybrids of Nicotiana1" it seemed desirable to grow a considerable number of plants in sand cul- tures which would vary widely both as to the principal nutrient I elements, nitrogen, phosphorus, and potassium, and as to the total concentration of all of the nutrient salts. The marked influence of the nutrient factors upon the growth of the plaid has afforded an excellent opportunity for a somewhat detailed study of the influence of the composition and concentration .of the nutrient solution upon the growth of one of the higher seed- plants of herbaceous character. ~ Hall, Brenchley, Underwood, Jour. Agric. Sei., vol. 6, pp. 278-301, 1914. s Shive, Physiol. Res., vol. 1, pp. 327-396, 1915. 9 Birner and Lucanus, Landw. Versuchsstat., vol. 8, pp. 1 US— 1 77, 1886. 10 Goodspeed and Ayres, Univ. Calif. Publ. Bot., vol. 5, no. 9, 1916. 344 University of California Publications in Agricultural Sciences [Vol. 1 The Use of Sand as a Culture Medium The ease with which solutions can be prepared and subse- quently analyzed has made the water-culture method especially desirable in investigations of the role of nutrient substances in plant growth. A solution has generally been recognized, how- ever, to be otherwise undesirable as a medium for the growth of the higher plants, since the root system is kept, during the course of the experiment, in an unnatural environment. Thus, while this method serves admirably for analytical purposes, it seems probable that the plant thus subjected to an unnatural environ- ment will suffer certain more or less serious physiological dis- turbances. In this connection, it is a well-established fact that the development of root hairs is much greater in sand than in water,11 the resistance of the substratum favoring root-hair pro- duction.12 Roots in general grow longer and thinner in water than in sand or moist soil. Hall, Brenchley, and Underwood13 think that the more vigorous growth of barley in sand, as com- pared with water cultures, is due to more efficient aeration of the former. It would seem, therefore, that sand is preferable to water as a culture medium, since in sand cultures the physical conditions present about the root system more nearly simulate those found in the soil. It is still a question just what part these physical conditions may have in plant nutrition. Undoubtedly such physical reactions as capillarity14 and adsorption18 must be important factors, since both the absorption and availability of nutrient salts would be affected by these physical phenomena. Breazeale1" has shown that the effect of concentration in sand cultures is very different from that in water cultures, the best concentration for wheat in water being three hundred parts per million, while in sand it is in the vicinity of two thousand five hundred parts per million, an effect which is no doubt largely due to the adsorption of certain salts or ions by the sand particles. 11 Sehwarz, Bot. Inst. Tubingen, vol. 1, pp. 135-188, 1883. 1= Snow, Bot. Gaz., vol. 40, pp. 12-43, 1905. is Loc. cit. i* Bell and Cameron, Jour. Phys. Chem., vol. 10, p. 659, 1906. is Sehreiner and Failyer, U. S. Dept. Agrie. Bull. 32, 1906. i'1 Breazeale, Science, n. s., vol. 22, pp. 146-149, 1905. L917] lyres: Nutrient Solution on Plants Grown in Sand Cultures 345 The physical effects of sand as a medium for planl growth have been shown recently in a striking manner by McCall,11 who added to saml tin- solutions which Shive18 used as water cultures, with the resull thai much larger quantities of the nutrient salts were required than when the same species of plant was grown in water culture. The sand-culture method was selected for the present work with the above evidence in mind, and also because the growing period of the tobacco plant is long and 1 his method precluded the tedious changing of solutions necessary when the water-culture method was used. Experimental Material The planl which was used in the present series of investiga- tions was a tobacco of hybrid origin derived from a cross between Nicotiana sylvestris (U. C. B. G. 69/09) and Nicotiana tabacum var. macrophylla (U. C. B. G. 22/07) and known in the Tni- versity of California Botanical Garden as U. C. B. G. H38.1S The plants to be used were raised from seed and were transferred as seedlings to the sand from the flats in which they were grown after carefully washing the roots free from adhering soil par- ticles. In picking out seedlings from the flats care was taken to choose from the large numher of plants available only those which were most nearly uniform with reference to size and general appearance. The plants were kept during the experiment in a well-ventilated greenhouse. The sand used was a light-colored beach sand which on analysis by means of the acid-digestion method of Hilgard showed the following composition: Fe,0; 0.592 per cenl P.,0, 0.004 per cenl U,0, 0.46 pen-out MgO 0.28 per cenl K,<> Trace CaO 0.06 per cent The water-holding capacity was 22 per cent when saturated. The sand was prepared for the experiment by washing in a heavy stream of tap water which was allowed to percolate through 17 Unpublished work. i^ Loc. cit. i»Setchell, Univ. Calif. Publ. Bot., vol. 5, pp. 1 B6, 1912. 346 University of California Publications in Agricultural Sciences [Vol. 1 a column of the sand for a period of twenty-four hours. The excess of tap water retained by the sand was in turn washed out with distilled water. While this sand is inferior to the best grade of pure quartz sand in freedom from inorganic material, it is unable to supply available nutrient elements in sufficient quantity to cause any perceptible increase in growth (pi. 14). Two thousand gram portions of the sand treated as above were weighed into six-inch flower-pots winch had been previously prepared by dipping them into melted paraffin. The paraffining effectually closed the pores and prevented the absorption of the culture solution by the pot. Distribution op Nutrient Salts The pots were divided into three different groups designated as series I, II, and III, each series consisting of twenty pots divided into groups of five pots each, and a duplicate in each case, making forty pots in all in each series. In series I, nitrogen, as NaN03, was the varying factor within each group, the weight of each of the other salts being held constant. Thus, in series I, the pots 1 to .5 in each of the four groups contained NaN03 as follows: 0.02, 0.2, 1.0, 2.0, 3.0 grams. In a similar manner phos- phorus and calcium, as Ca(H2P04)2, were varying factors in series II, while in series III potassium, as K2S04, was varied. As noted above, the twenty plants of each series were divided into four groups designated respectively as A, B, C, and D, each group consisting of five plants and a control for each. The weight of one varying factor remained the same in pots of like number through all four groups. Thus plants I A 1, I B 1, I C 1, and I D 1 each contained 0.02 grams of NaNO,, and I A 2, 1 B 2, I C 2, and I D 2 contained 0.2 grams of NaNO:.. But from group A to D the weight of the other nutrient factors decreases, so that group D contains two-thirds, C one-half, and D one-fourth the weight of each of these nutrient factors as present in the A group. The effect of this distribution of salts is to give at least three important variables. First, the single nurient salt in increasing proportions from plant 1 to plant 5 in each group, and second, the factor of total concentration which decreases from group A l!U7| Ay res: Nutrient Solution on Plants Grown in Sand Cultures 34' to group D in each scries. The third important variant, the balance of sails in the solution, follows as a matter of necessity, since the single nutrient salt added in increasing quantities from plant 1 to plant 5 is added with uniform variation and in the same quantity in each group, while the quantities of the other salts, although constant within a group, are not constant within all TABLE 1 w i ii.mt in Grams of Salts Added to Each Pot Containing 2000 Grams of Sand (In the following table the reman numerals indicate the series numbers, ami the letters are those of the corresponding groups.) o O « d DO = W o* CO . s 6 x - 0 = z? d 3& d = w 5 «fG - v. c £ x - o c « 3 6 c dl y. r- d - cc da C - C C e2- IA1 .02 1.2 2.4 .96 1.5s 11C1 1.5 .02 1.2 .48 3.20 IA2 .2 1.2 2.4 .96 4.76 IIC2 1.5 .10 1.2 .48 3.28 [A3 1.0 1.2 2.4 .96 5.56 IK':: 1.5 .20 1.2 .48 3.38 IA4 2.0 1.2 2.4 .96 6.56 1IC4 1.5 1.0 1.2 .48 Lis EA5 3.0 1.2 2.4 .96 7.56 IIC5 1.5 2.0 1.2 .48 5.18 IB1 .02 .8 1.6 .64 3.06 IID1 .75 .02 .6 .24 1.61 1 B2 .2 .8 1.6 .64 3.24 IID2 .75 .1 .6 .24 1 .69 [B3 1.0 .8 1.6 .64 4.04 l in:; 75 .2 .6 .24 1.79 IB4 2.0 .8 1.6 .64 5.04 IID4 .75 1.0 .6 .24 2.59 [B5 3.0 .8 1.6 .64 6.04 [ID5 .75 2.0 .6 .24 3.59 IC1 .02 .6 1.2 .48 2.30 IIIA1 3.0 1.2 .02 .96 5.18 IC2 .2 .6 1.2 .48 2.48 TI1A2 3.0 1.2 .10 .96 5.26 [C3 1.0 .6 1.2 .48 :;.2s IIIA3 3.0 1.2 .20 .96 5.36 IC4 2.0 .6 1.2 .48 4.28 IIIA4 3.0 1.2 1.0 .96 6.16 IC5 3.0 .6 1.2 .48 5.28 IMA.", 3.0 1.2 2.0 .96 7.16 11)1 .02 ..". .0 .24 1.16 1IIB1 2.25 .8 .02 .64 3.71 11)2 2 .3 .6 .24 1.34 IIIB2 2.25 .8 .10 .64 3.79 ID3 1.0 .3 .6 .24 2.14 II1B3 2.25 .8 .20 .64 3.89 ID4 2.0 .3 .6 .24 3.14 1 1 1 B4 2.25 .8 1.0 .64 4.69 ID5 3.0 .3 .6 .24 4.14 1 1 1 1 15 2.25 .8 2.0 .64 5.69 TTA1 3.0 .02 2.4 .96 6.38 IIH'l 1.5 .6 .02 .48 2.60 IIA2 3.0 .10 2.4 .96 6.46 niC2 1.5 .6 .10 .48 2.68 HA3 3.0 .20 2.4 .96 6.56 [IIC3 1.5 .6 .20 .48 2.78 TTA4 3.0 1.0 2.4 .96 7.36 1 1 1 ( '4 1.5 .6 1.0 .48 3.58 IIA5 3.0 2.0 2.4 .96 8.36 1 1 1 C5 1.5 .6 2.0 .48 4.58 [IB] 2.25 .02 1.6 .64 1.51 1111)1 .75 .:{ .02 .24 1.31 1 1 B2 2.25 .10 1.6 .64 t.59 [IID2 .75 .:: .10 .24 l.::<» 1 1 B3 2.25 .20 1.6 .64 4.69 nil).', .75 .3 .20 .24 1.49 ! 1 1 : t 2.25 1.0 1.0 .64 5.49 iiidi .75 .:i 1.0 .24 2.29 1 1 1 ::, 2.25 2.0 1.6 .64 6.49 1 1 1 1 ».-, .75 .3 2.0 .24 3.29 348 University of California Publications in Agricultural Sciences [Vol.1 the groups of a series. Thus I A 5, IBS, I C 5, and I D 5 each contained 3 grams NaNO.,, but the content of each pot in K2S04 was 2.4, 1.6, 1.2, and 0.6 grams, respectively; hence the balance between NaNO:, and K._,S04 is very different in each of the four pots. Table 1 shows the distribution of the salts in the three series and the total concentration in grams of the salts in each pot. The total quantity of nutrient salts was added to the sand at the beginning of the experiment. The plants were placed in the sand June 15 and were har- vested about November 1, the tops and roots being kept for the determination of dry weight.20 It will be seen that the plant was allowed sufficient time to complete its natural period of growth, thus permitting certain observations of a quantitative nature as recorded in table 2. PHYSIOLOGICAL EFFECT OF NITROGEN Distribution op Salts in Series I In series I nitrogen as NaNO:, was the salt which was used in the same weights in all of the four groups A, B, C, and D, being present in pots 1 to 5 as follows: 0.01 g. (.001 per cent), 0.2 g. (.01 per cent), 1.0 g. (.05 per cent), 2.0 g. (.1 per cent), 3.9 g. (.15 per cent). The maximum weights of other salts were Ca(H2P04)2, 1.2 g.; K2S04, 2.4 g. ; MgS04, 0.96 g., in group A, while the minimum quantity of these salts as added in group D was 0.3 g., 0.6 g., and 0.24 g., respectively. The total concen- tration in this series ranged from 1.16 g. in I D 1 to 7.56 g. in I A 5. Height in Series I The height of each plant was measured at two different periods. The first measurement was made when the majority of the plants were just beginning to show the first signs of flower- bud formation. The second measurement was taken five or six weeks later, when most of the plants were in full bloom. The final height of the five plants in each group is shown graphically 20 An accident to the roots while drying prevented the collection of further data on their dry weight. 1 !• 1 7 1 Juris: Nutrient Solution on Plants Grown in Sand I ultures 349 TABLE 2 Si MM.UIV OF QUALITATIVE AND Ql \ '. ill 'ATIVE Data for EACB PLANT in the following table the roman numerals indicate the series numbers, iiinl the tetters are those of the corresponding groups. Leal i , .,i Dry Pot Height, length, width, \ umbi i Number u e in No. cm. m cni. lea\ es flowers tups, gms. IA1 2.5 7.6 3.7 (i. 0. L.12 IA2 4.5 9.6 1 7 7. 0. L.60 I \ 1 8. lL'.l 6.2 10.5 0. 1.56 l.\l 57.5 L3.8 9.5 17. 25.5 IA5 15.5 20.8 10.2 17.5 24. 7.83 MM ->.:, !•.:, 4.9 7.5 0. 1.29 TB2 3.5 8.6 4.1 7. 0. l.Ui II:;: 8. 12.1 5.5 9. 1. 2.17 1R1 7s. L8.8 9.5 17.5 29. 8.57 1 nr. 19. 19.9 10.1 1 7.5 21. 7.96 K'l 3.5 8.8 4.3 C.5 0. .71 Hi' 2.5 8.3 4.3 6. 0. .79 ]c:: 4.5 11.2 5.6 7. 0. L.65 K'l 94. 19.5 9.7 17.15 31.5 l < 15 74. 18.7 9.1 18. 29. 9.24 1 1 > l 6.5 in..-. 5.4 7. 0. 1.65 TD2 1 7..-» 12.7 6.3 9.5 0. L.53 [D3 59.5 15.8 7.8 15. 8.5 5.86 MM 91.5 14.6 7.7 19. 34.5 11.12 1 1 >5 66.5 17.:: 8.6 18.5 2 1 .5 7.60 TTA1 15. L2.9 6.4 12. 0. 2.09 IIA2 55. 1 8.5 8.4 15.5 1 1.5 6.21 II A:: 69.5 18.9 9.4 16.5 22.5 8.75 1 1 A 4 87. 19.2 9.7 KI.5 25.5 S.5S IIA.-i 73. 18.9 9.3 16.5 29. 8.60 [IB] 21. i::.l 6.1 12. 0. 2.71 HB2 35.5 15.3 7.3 1 1.5 4.5 3.82 111::: 43. 15. 7.4 14. 9.5 4.1 1 1 B4 97. Is.:: 9.3 1 8.5 37. 9.3 ! 1 1 15 74.5 18.6 9.6 17. 23.5 7.76 IK'l 13.5 12.2 5.9 11. 0. 2.73 IIC2 27.5 L3.9 6.6 12. 3. 3.22 lie:: 101. L6.5 8.2 17.5 34 5 8.20 IK'l 90. 17.3 8.9 17. 32. 8 66 1 1 ( ■:, 78. 17.1 8.3 18. 26.5 7.88 nni 18. 12.8 6. 1 1 .5 2.5 2.47 JID2 I',!.:, 14.8 7.4 15.5 15. 5.83 IID:: 71. l. ;.:, 7.6 16. 19.5 6.27 IIIM 83.5 l 1.2 7.5 17.5 28. 7.60 1 1 1 »5 Mi. L3.9 7.2 17. 19. 6.75 1 1 1 A 1 56.5 L6.7 8.0 1 1 5 6.5 t.65 [IIA2 Mi.f, 20. 10.1 16.5 27. 7.88 III A:: 62. L'n. 7 9.6 17.5 14. 6.97 IIIAI 74. 20.2 Id. 17. 20.5 10.53 [IIA5 63. 22.1 1(1.5 17. •_'l. s.l 1 350 University of California Publications in Agricultural Sciences [Vol. 1 TABLE 2— (Cc mtinued) Leaf Leaf Dry Pot Height, length, width, Number Number weight No. cm. cm. cm. leaves flowers tops, gins IIIB1 81.5 19.9 10.1 17. 22. 8.18 IIIB2 87. 20.3 10. 17.5 24. 5.87 IIIB3 94.5 18.3 9.4 17.5 31. 8.4 IIIB4 83. 19.1 9.7 18. 26.5 4.86 IIIB5 77.5 18.8 9.7 17. 39.5 8.42 IIIC1 89. 18. 9. 17. 18. 6.58 IIIC2 102. 17.7 8.8 17.5 22.5 8.57 IIIC3 109. 17.4 8.9 18. 23. 9.4 IIIC4 88.5 18.5 9.2 17.5 25. 7.66 IIIC5 79. 17.2 8.8 18. 26.5 8.68 IIID1 89. 16.4 8.2 17. 14. 5.6 IIID2 103.5 15.1 7.8 18. 17.5 7.27 IIID3 100.5 15.9 7.8 17.5 16.5 6.96 IIID4 90. 16.5 8.2 17.5 23. 6.75 IIID5 66.5 17.5 8.7 17.5 19. 6.36 in figure 1. As two plants were given similar treatment in each case, the height as noted in table 2 is the mean of the height measurements of these two plants. in 90 - /I 80 70 - ' l i 6C - // - N N N -« S 50 * / // /^ / 1 / ^■~~~~^A 40 / / l< / 30 20 / / / / V 11/ '/ 10 7 / ' ' i i , .001 .01 .05 .1 .15 % NaN03 Fig. 1. — Graph showing the influence upon height of equal quantities of NaN03 in the different groups of series I. 1!U7| Ayres: Nutrient Solution on Plants Grown in Sand Cultures ; i ."> 1 The effect of increasing the <|u;uit il >• of nitrogen from planl 1 to planl 1 is marked in all groups. In every group plant 5 is not so tall as plant 4 (pi. 5), hence it would socio that the optimum nitrogen supply for tobacco growing in sand cultures, with height as an index, is somewhere near 0.1 per cent of NaNO:!, calculated on the basis of the dry weight of the sand. Cm. 60 70 Dg. total concentration Fig. 2. — Graph showing the Influence of total concentration upon height in series I. There is slight variation in the first three plants of groups A, B, and C, showing that change in the total concentration of the solution within these limits does not affect the characters of the plants to any great extent. This, however, does not apply to group D, in which the total concentration is low (1.16 to 4.14 g.), for plants 2 and 3 are far superior to the corresponding plants of the other groups, although Hie nitrogen content is exactly the same. When the nitrogen content is at or near the 352 University of California Publications in Agricultural Sciences [Vol. 1 optimum the influence of concentration on height is exhibited in a more uniform manner, as shown in plants 4 and 5 of all groups (pi. 6). Plants growing in the solution of lower concen- tration, in general, are taller than those growing in the solutions of higher concentration. The influence of total concentration upon height of plant when taken in connection with optimum and deficient nitrogen supply is indicated in figure 2, which shows a curve for each of the two measurements made on each plant, the upper curve being plotted from the last measurements taken. This curve is espe- cially interesting since it shows the influence of nitrogen as a prime factor in growth in solutions which are of approximately the same concentration. Thus in I D 4 and I B 1, where the total concentrations are 3.14 g. and 3.06 g., the heights of the two plants are 91.5 cm. and 5.5 cm. Such a large difference can be due in this case only to the lack of nitrogen in I B 1, since there is present a considerable excess of the other nutrients required (pi. 7). A study of the early and late height curves shows that the plant responded very early to the amount of salts available, as is indicated by the similarity of the early curve to that based upon the later measurements. The greatest final height is at- tained, as was to be expected, through the continuous growth of those plants which had sufficient nitrogen, while the growth of the under-nourished plant was decidedly retarded. Thus at the end of the growing season the differences in height between the two groups became more marked as the time of complete maturity drew near. Attention is called to this fact since it is not an uncommon practice in growing plants in water cultures to harvest them before maturity. While these plants might give an index of the influence of the culture solution on growth, they would not give a true value for the nutritive function of the solution, since increase might persist for a considerable time in solutions of optimum nutritive value while plants growing in an unfavorable medium would be practically at a standstill. l!M7| lyres: Vutrieni Solution on Plants Grown in Sand Cultures l>i;v Weight in Series I A comparison of the curves for heighl (fig. 1) and for <\ry weighl (fig. 3) shows that in a general way heighl is an index to the dry weight. This fad is more marked in this scries than in either series II or III since the plants were more uniform throughout the series, being uniformly stocky where the heighl was above 40 cm. In the other groups some of the plants were l lecigi 1 >r\ wt. of tops 1 1 o In, / ""'Vs. 91 ■ y ^"^".^ 80 ■ / ^^ 70 y / S" Z^< CO ■ / S* 50 / / ^' 40 ,/ / ^ ^ — 30 / / A 20 s B y -Ss£^ _ C 10 — ,/' _ — ""■ _D *r-±-- , — ' — " ^~" .001 .01 .05 .1 .15 ■ . NaNOa Fig. 3. — Graph showing influence of equal quantities of NaNO:. in the different groups of series I upon dry weight of tops. tall and very spindly (pi. 15), and there was a marked decrease in the length and width of leaf, which would, of course, lower the dry weight. The height measurements even on a plant of the habit of the tobacco cannot be taken alone as an indication of the nutritive value of a solution, a fact which has been shown to hold true to a much more noticeable extent in such plants as wheat, which will stool more in some cultures than in others without perceptible differences in height. The effect of the concentration is evidenced in the curve for group D, which is much higher for plants 3 and 4 than for plants of like number in any other groups. Had it been possible to take 354 University of California Publications in Agricultural Sciences [Vol. 1 the dry weight for plant I C 4 this weight would probably have been slightly greater than that of I D 4 (see table 2), making the curves correspond to those for height. THE INFLUENCE OF THE CULTUEE SOLUTION ON FLOWEE PEODUCTION Our information concerning factors which may influence flower formation is very incomplete. Vochting21 has demon- strated that light intensity is a factor in flower development in Mimulus, and numerous other plant physiologists have found that a more or less marked influence on flower formation could be correlated with some external factor. The relation to the formation of flowers of nuti'ient salts in the medium in which growth takes place seems never to have been studied in any thoroughgoing manner. Mobius22 found that certain Oramineae flowered better on dry soil and on soil low in nutrient elements than on soil rich in nutrients and where water supply was abundant. Jost23 thinks that the fact that root pruning increases flower production may be thus explained, since there is a lower- ing of the absorptive capacity of the tree for inorganic salts. There has been also a general opinion, which is not fully justified, that any condition which will cause marked vegetative develop- ment will retard flower production. The experiment herein re- ported has presented an opportunity for a study of the influence of the composition and concentration of the solution upon flower production. In the plant used in this experiment the flowers fall soon after opening, leaving a scar upon the inflorescence stock.24 At the end of the growing season the number of flowers produced by each plant was determined by counting these scars (see table 2). The total number of flowers produced by each plant is shown diagrammatically in figure 4. 2i Vochting, Jahrb. f. wiss. Bot., vol. 25, p. 149, 1893. 22 Mobius, Beitr. z. Lehre v. d. Fortpflanzung d. Gewachse, Jena, 1897. 23 Jost, Lectures on plant physiology, p. 364, 1907. 24 Goodspeed and Ayres, Univ. Calif. Publ. Bot., vol. 5, no. 9, 1916. 1017 | Ayres: Nutrient Solution on Plants Grown in Sand Cultures 355 .i.z.Jt^li^l^Ukli.g.JHbli^l^UN jhbM'ibLi'NilbMslibbUj li bbUlai bbULsl i bbUNi I2I3I4I5 Group j\ B C Series I ABC Series II A B c D Series III Fi£. 4. — Diagrammatic representation of the number of flowers produced by each plant in series I, II, and 111. Flower Production in Series I The nitrogen supply is seen to have a very definite influence upon flower production. In series I no flowers were produced by plants 1 and 2 of any group and in only two groups were any flowers produced by plant 3, showing definitely that unless nitrogen is present in excess of 0.05 per cent as NaNO:i the under- nourished tobacco plant will not flower. Flower production in 356 University of Col i font ia Publications in Agricultural Sciences [Vol.1 general corresponded to vegetative vigor, the plant exhibiting maximum vegetative growth producing the largest number of flowers. Here again the influence of the total concentration of the solution was apparent in the flower yield in the various groups, which increased as the concentration decreased. Cm. 100 ~~~"""-^ '"'v 90 1 ^ 7^-l\ 80 "f / 70 fiO - \h ' 1 ' \ ' 1 1 ;>o 11 <' \\\ / • 1 ' 1 / 40 If :io r f V 20 1 \ 10 1 — 1 1 1 1 g g S .05 .1 '/( CafH-.PO^j o o ■ Fig. 5. — Graph showing the influence upon height of equal quantities of Ca(H2P04)2 in the different groups of series II. PHYSIOLOGICAL EFFECT OF PHOSPHORUS Distribution op Salts in Series II In series II a study was made of the influence of phosphorus added as Ca(H2P04)2. This salt was present in the same quan- tity in all groups A, B, C, and D, the quantity in each of the pots 1 to 5 being 0.02 g. (.001 per cent), 0.1 g. (.005 per cent), 0.2 g. (.01 per cent), 1.0 g. (.05 per cent), 2.0 g. (.1 per cent), 1917] Ayres: Nutrient Solution on Plants Grown in Sand Cultures '■'•'<• respectively. The maximum weights (if (lie oilier sails were NaN03, :: g. ; K so,. 2.4 g.; MgS04l 0.96 g., in group A, while the minimum quantities of these salts as added in group D were 0.7") g., 0.6 g.. and 0.24 g., respectively. The total concentration in this scries ranged from 1.01 g. to <>.:>s <>■. 10 - 70 80 Us. total concentration Fig. 6. — Graph showing the influence of total concentration upon height in series II. Height in Series 11 Figure 5 shows the height curves for the five plants of each of the four groups in this series. There is clear indication thai the optimum phosphorus supply lies somewhere between .05 per cent and .01 per cent of Ca(H2P04)2, the heighl of plant 4 heing greatest when all groups are considered. The difference in height between plants 4 and 5 is not great in any group. The effect of increasing the quantity of Ca(H2P04)2 is clearly seen in plants 1, 2, 3, and 4 of groups A, B, and D (pi. 8). The effect of t ota I 358 University of California Publications in Agricultural Sciences [Vol.1 concentration in this series is not so marked as in series I, but is slightly evidenced in the somewhat better growth of some of the plants in groups C and D as compared with plants in groups A and D (pi. 9). The height of the plants at two different periods in their growth was taken in this series at the same time that the measurements were taken in series I and plotted against total concentration (fig. 6). The total concentration of salts in the solution is here, as in series I, of secondary importance when one element is present in insufficient amount, as will be seen (pi. 6) when plant II C 1 (3.20 g.) is compared with II C 3 Decigrams. Dry wt. of tops 100 .l'i Ca(H2P04)L. Fig. 7. — Graph showing the influence on dry weight of tops of equal quantities of Ca(H2P04), in the different groups of series II. (3.38 g.). While the total concentration is practically the same and the total quantity of each of the other salts is the same the Ca(H.,P04)1, in II C 3 is ten times the quantity of the same salt in II CI. Dry Weight in Series II A comparison of height (fig. 5) and dry weight curves (fig. 7) for tops in this series shows that height here is not an accurate index to dry weight. Thus group A gave the greatest total dry weight, while the greatest total height of plants occurred in group D, a fact which is explicable since very serious injury resulting in a spindly habit was shown by many plants in the D group, as will be pointed out later in the discussion of injury due to the improper balance of salts in the solution. L917] lyres: Nutrient Solution on Plants Groun in Sand Cultures 359 Flower Production in Series 1 1 The total number of flowers produced in this series was Larger ilian in series I. due largely to the fad thai there was less stunted growth in plants ]. 2, and 3 of each group, for which an ample supplj of nitrogen was available. Plants [I A 1, II B 1, and Ilt'l did not produce any flowers. The greatesl number of flowers was formed in group C and the greatesl yield of any one plant was given by II B 5. The flower yield in each group is definitely related to the general character of the plant as men- t ioned above in conned ion \\ ith series I. PHYSIOLOGICAL EFFECT OF POTASSIUM DisTinra thin op Salts in Skkiks I IT The plants in series III were grown to study the physiological influence of various quantities of potassium added as K.S(), in the presence of a sufficient supply of other nutrient sails, fol- lowing the same plan as outlined above for the variation of nitrogen and phosphorus in series I and II. K..XO, was present in the same weight in each of the four groups A, B, C, and I), the quantities added to each of the pots 1 to 5 being 0.02 g. (.001 per cent), 0.1 g. (.005 per cent), 0.2 g. (.01 per cent), 1.0 g. .()."> per cent), and 2.0 g. (.1 per cent). The maximum weights of the other salts were \'a.\<> , :; g.; Ca(HJPOJ2, 1.2 g. ; MgS04, 0.96 g., in group A. In group I) the minimum quantities of these salts were 0.75 g., 0.3 g., and 0.24 g., respectively. The total concentration in this series varied from 1.31 g. to 7.16 g. Height in Series III No plants in this series were less than f>0 cm. high, due to the fact that the two nutrient elements, nitrogen and phosphorus. which in the order named are of first importance as growth factors, were present in sufficient quantity to insure considerable growth (pi. 7). Only a small quantity of K,S04 (.005 to .01 per cent ) was required in this series to give plants of maximum In ight, hence the curves show a downward trend in all plants after either plant 2 or plant 3 in each group (fig. 8, also pi. 12). Thus it is evident that there is a toxic effect of an excess of potassium, irrespective of the total concentration of the solution. 360 University of California Publications in Agricultural Sciences [.Vol. 1 The influence of total concentration is again plainly seen in this series. Plate 13 shows plant 1 of each of the groups A, B, C, and D. As the total concentration decreases from A to C there is a steady increase in the vigor of the plant as judged by height. Curves in figure 9 indicate this general tendency to an increase of height with a decrease in the total concentration of the solution. Dry Weight in Series III As in series I and II, the dry -weight curves (fig. 10) do not correspond with the height curves (fig. 8). The greatest dry weight of any plant was that of III A 4, which was not so tall as the other plants of like number. The low dry weight of III B 4 is especially noticeable. A comparison of the two dry-weight curves for the A and B groups shows a very peculiar effect of K2S04 in solutions of different balance. In each case where the group A curve is high, the group B curve is low, a fact which also applies to plants 3, 4, and 5 in the A and C groups. That this should occur with such regularity is rather remarkable and no satisfactory explanation can as yet be found to account for this situation. It is evident that the physiological balance of salts in the solution is dependent upon the concentration, as has been shown by McCool,25 Gile,20 Tottingham,27 and Shive.28 Flower Production in Series III The more vigorous growth of plants in this series gave a greater total yield of flowers than either of the other two series. This was to be expected from the result of series I and II, where the flower yield was shown to be definitely related to the general vigor of the plants. The production of flowers in this series differs, however, from that in the other series. An increase of K.,S04, while in general depressing the total height of the plant, when added in excess of .01 per cent gave a higher flower yield. Thus in group C there is steady increase in the number of flowers produced which corresponds to the increase of K2S04. The 25 McCool, Cornell Agric. Exp. Sta. Mem., vol. 2, pp. 121-170, 1913. ze Gile, Porto Rico Agric. Exp. Sta. Bull. 12. 27 hoc. cit. 28 Loc. cit. 1917] Ayres: Nutrient Solution on Plants Grown in Sand Cultures 381 Cm. r ion % K2S04 Fig. 8. — Graph showing the influence upon heighl of equal quantities ,i|' K SO, hi tin' .lil't'rniit groups of series III. Cm. 110 90 so 60 in ::o jii J_ 20 30 10 50 60 70 Dg. total concentral ion Fig. 9. — Graph showing the influence upon height of total concentration in series III. 362 University of California Publication* in Agricultural Sciences [Vol. 1 greatest flower production occurred in group B, and plant 5 of this group produced a larger number of flowers than any other plant in any series. INJURY DUE TO EXCESS OR DEFICIENCY OF NUTRIENT SALTS The deficiency or excess of certain elements will cause injury which is very characteristic. Gris as early as 1843 showed that chlorosis was caused by a lack of iron in the nutrient solution. Nitrogen starvation likewise has long been known to cause chlo- rosis, a condition which may also result from an excess of soluble Decigrams. Dry wt. of tups Cm. ', K_.su, Fig. 10. — Graph showing the influence upon dry weight of tops of equal quantities of K_S04 in the different groups of series III. phosphate.29 Magnesium starvation results in injury to the chlorophyll bodies, and in excess is harmful unless antagonized by calcium.30 Other physiological disturbances not so well estab- lished as these mentioned have been considered to be associated with a deficiency or excess of nutrient elements. The most marked indication of the fact that certain cultures in this experiment did not furnish a normal medium for growth was seen in the chlorosis which is so characteristic of plants grown in solutions which are deficient in nitrogen. This type of injury was uniformly present in all cultures containing 1.0 g. or less of NaNO.,, but was especially marked in series I, plants 1, 2, and 3, of all groups. It is not possible to draw a sharp 29 Crone, Sitzungsber Neiderrhein. Ges. Nat.- und Heilk, Bonn, 1902, pp. 167-173. 3»Loew and May, U. S. Dept. Agrio. Bur. Plant Ind. Bull. 1, 1901. L917] lyres: Vutrient Solution on Plants Grown in Sand Cult 363 line which will clearly segregate the injury to the various plants of a Large scries of this kind into well-defined groups since there is always more or less overlapping. An attempt was made, how- ever, to divide the plants into groups which would shew in each case a characterisl ic type of injury. (a) This »roup was made up of plants which were very much stunted, being less than 8 cm. in heighl and in every ease showed a marked chlorosis which was clearly attributed to a low supply of nitrogen. The plants in this group were I A 1, I A 2, I A 3, I B 1. I P. 2, I B3, [CI, 1 C2, I C3, 1 I) 1. (b) This group was somewhat taller, from 13 to 21 cm. high, hut clearly stunted in growth. These plants showed less chlo- rosis, since nitrogen was present in sui'licient quantity to provide close to the optimum supply in all cultures with the exception of II I) I and I 1)2, where there was a distinct chlorosis due to the low nitrogen supply. Plants showing this type of injury were II A 1, II Bl, II CI, II Dl, ID 2. (c) Plants in this group showed a more serious type of injury than any of the other plants. They were more than 40 cm. in height, but were very spindly (pi. 15). The whole plant showed marked chlorosis, which affected the lower leaves most severely and soon resulted in their death. This type of plant was found in cultures [ D 3, II B 2, II B 3, II C 2, 111)2. [I D 3, 1 1 D 4, III 1) 1. Ill 1)2. Ill 1)3, HID 4, and III D 5. (d) The plants of this group were decidedly more vigorous than those of the preceding groups, as indicated by their in- creased height and better color. Indeed, they seemed to he per- fectly normal. The following cultures were classed in this group : IC4, 11)4, lie:?, IIC 4, II D 5, III A 1, III A 2, III A 3, Til B 1. IIIB2, IIIB3, III CI, III C 2, III C 3, I1IC4, [II C 5 The following plants were even better in appearance than those just named : I A 4, I A 5, I B 4, I B 5, I C 5, I D 5, II A 2, II A 3, II A 4, II A 5, II B 4, II B 5, II C 5, 1 1 1 A 4. Ill A 5, 1 1 1 P» 4. III B 5. A study of the above grouping indicates that chlorosis was present wherever the nitrogen content was low, as was to be ex- pected. The spindly growth characteristic of groups II D and III I) may also be due to the low supply of nitrogen. It seems 364 University of California Publications in Agricultural Sciences [Vol. 1 that the injury which was so marked in series II must be in some way associated with the calcium-magnesium content in solutions which were not properly balanced. No definite calcium-magne- sium ratios can be found which are responsible for the injury which occurred in this series. Twenty different calcium-magne- sium ratios ranging from 0.035 to 3.54 occur in the series, and both plants which were normal and plants which were seriously injured were found in cultures in which the calcium-magnesium ratio was low as well as in cultures where this ratio was high. No definite conclusions can be drawn in this connection, however, since the other variables present complicate the situation so that the injury cannot be said with certainty to be associated with an improper balance between the calcium and magnesium. TABLE 3 Summary of Complete Experiments Grouped in such a manner that comparison can be made with special reference to the influence of concentration and balance of the solution upon crop and flower production. The calculation of the per cent total concentration is based on the assumption that the salts are all dissolved in the quantity of water held by 2000 grams of sand when saturated. To get this value in parts per million, multiply the total concentration in grams by 227.2. The real concentration would be much greater than these values would indicate, since the sand was not kept saturated. Series I « et o P. o £ >, O oa « CD CO da _-a o a a ~ r-'S 5 u •V to ~a U 5° £ 5" 73 ? if Si 3 ♦J u o M EH — R GQ +2 o - s 8 at C bo EH TA1 .02 .001 1.2 2.4 .96 4.58 1.04 2.5 1.12 0. IB1 .02 .001 .8 1.6 .64 3.06 .69 5.5 1.29 0. IC1 .02 .001 .6 1.2 .48 2.30 .52 3.5 .74 0. ID1 .02 .001 .3 .6 .24 1.16 .26 6.5 1.65 0. IA2 .2 .01 1.2 2.4 .96 4.76 1.08 4.5 1.6 0. IB2 .2 .01 .8 1.6 .64 3.24 .73 3.5 1.40 0. IC2 .2 .01 .6 1.2 .48 2.48 .56 2.5 .79 0. ID2 .2 .01 .3 .6 .24 1.34 .30 17.5 1.53 0. IA3 1.0 .05 1.2 2.4 .96 5.56 1.26 8. 1.56 0. IB3 1.0 .05 .8 1.6 .64 4.04 .91 8. 2.17 1. IC3 1.0 .05 .6 1.2 .48 3.28 .74 4.5 1.65 0. ID3 1.0 .05 .3 .6 .24 2.14 .48 59.5 5.86 8.5 IA4 2.0 .1 1.2 2.4 .96 6.56 1.35 57.5 25.5 IB4 2.0 .1 .8 1.6 .64 5.04 1.14 78. 8.57 29. IC4 2.0 .1 .6 1.2 .48 4.28 .97 94. 31. ID4 2.0 .1 .3 .6 .24 3.14 .71 91.5 11.12 34.5 IA5 3.0 .15 1.2 2.4 .96 7.56 1.71 45.5 7.83 24. IB5 3.0 .15 .8 1.6 .64 6.04 1.37 49. 7.96 21. IC5 3.0 .15 .6 1.2 .48 5.28 1.20 74. 9.24 29. ID5 3.0 .15 .3 .6 .24 4.14 .94 66. 7.60 21.5 1917] Ayres: Nutrient Solution on Plants Grown in Sand Cultures 365 Series II d o ©■a • p. OS y. - <*5 GO ■j: 2 oa x a eg ss Eh — E o » - U .10 .005 .75 .6 .24 1.69 .38 64.5 5.83 15. IIA3 .20 .01 3. 2.4 .96 6.56 1.49 69.5 8.75 22.5 J I ]',.'. .20 .01 2.25 1.6 .64 4.69 1.00 43. 4.11 9.5 IIC3 .20 .01 1.5 1.2 .48 4.18 .94 101. 8.20 17.5 IID3 .20 .01 .75 .6 .24 2.59 .58 74. 6.27 16. IIA4 1.0 .05 3. 2.4 .96 7.36 1.67 87. 8.58 25.5 IIB4 1.0 .05 2.25 1.6 .64 5.49 1.24 97. 9.3 37. I KM 1.0 .05 1.5 1.2 .48 4.18 .95 90. 8.66 32. IID4 1.0 .05 .75 .6 .24 2.59 .58 83.5 7.60 28. IIA5 2.0 .1 3. 2.4 .96 8.36 1.90 73. 8.60 29. IIB5 2.0 .1 2.25 1.6 .64 6.49 1.47 74.5 7.76 23.5 IIC5 2.0 .1 1.5 1.2 .48 5.18 1.17 78. 7.88 26.5 1 1 1 )5 2.0 .1 .75 .6 .24 3.59 .81 86. 6.75 19. Series III to £ - s O S d (S5 da a51 CO _-a ~ ~- O &) Eh - 5 r. V U 5 — O ta |.Sa ha • ■ss •3 ft o Eh o IIIA1 .02 .001 3. 1.2 .96 5.18 1.17 56.5 4.65 6.5 IITB1 .02 .001 2.25 .8 .64 3.71 .84 81.5 8.18 22. ITIC1 .02 .001 1.5 .6 .48 2.60 .59 89. 6.58 18. IIID1 .02 .001 .75 .3 .24 L.31 .29 89. 5.56 14. IIIA2 .1 .005 3. 1.2 .96 5.26 1.19 82.5 7.88 27. TIIB2 .1 .005 2.25 .8 .64 3.79 .86 87. 5.87 24. IIIC2 .1 .005 1.5 .6 .43 2.68 .60 102. 8.57 22.5 IIID2 .1 .005 .75 .3 .24 1.39 .31 103.5 7.27 17.5 IIIA3 .2 .01 3. 1.2 .96 5.36 1.21 62. 6.97 14. IIIB3 .2 .01 2.25 .8 .64 3.89 .88 94.5 8.4 31. IIIC3 ,2 .01 1.5 .6 .48 2.78 .63 109. 9.4 23. IIID3 .2 .01 .75 .3 .24 1.49 .33 100.5 6.9 16.5 IIIA4 1.0 .05 3. 1.2 .96 6.16 1.40 74. 10.53 20.5 II1B4 1.0 .05 2.25 .8 .64 4.69 1.06 83. 4.86 26.5 IIKM 1.0 .05 1.5 .6 .48 3.5.8 .81 ss.;, 7.66 25. I1ID1 1.0 .05 .75 .3 .24 2.29 .52 90. 6.75 23. IIIA5 2.0 .1 3. 1.2 .96 7.16 1.62 63. 8.11 24. I1IB5 2.0 .1 2.25 .8 .64 5.69 1.29 77.5 8.42 39.5 ITIC5 2.0 .1 1.5 .6 .48 4.58 1.04 79. S.liS 26.5 IIID5 2.0 .1 .75 .3 .24 3.29 .74 66.5 6.36 19. . 366 University of California Publications in Agricultural Sciences [Vol. 1 THE ABSORPTION OF SALTS FROM THE CULTURE MEDIUM The absorption by plants of salts from a solution is no doubt intimately related to the composition of the solution, since the intake of inorganic salts occurs only when the concentration of the solute outside the permeable protoplast is greater than that within. Hence the total osmotic concentration of a solution may affect the intake and storage of the salts from the solution.31 The quantity of salts which are absorbed by the plant may also vary with the qualitative composition of the solution. Thus True and Bartlett82 have shown that absorption from a solution of two or of three salts is more rapid than from a solution containing a single salt. It is evident that the factors which regulate ab- sorption are very complex, and that this complexity increases with an increase in the number of different anions and cations in the solution. It is further evident that two methods may be followed with a view to ascertaining the quantities of salts ab- sorbed. The ash of the plants may be analyzed or the residue of salts remaining in the culture may be determined. It has seemed desirable to attempt a study of absorption in the present case by means of the latter method. Method of Analysis The small quantities of salts added to each pot made the acid-extraction method undesirable, since the large quantities of sand required to give weighable precipitates would have been extremely hard to dehydrate, thus introducing a considerable source of error. For this reason the colorimetric method of analysis13 was used in this work. An exception was made in the determination of calcium, which was made by the usual volu- metric method. The sulphur was determined gravimetrically as BaS04. A water extract was prepared from 250 g. of sand by leaching with successive small portions of distilled water until si Livingston, The role of diffusion and osmotic pressure in plants, Chicago, 1903. 32 True and Bartlett, U. S. Dept. Agric. Bur. Plant Ind. Bull. 231, 1912, and Am. Jour. Bot., vol. 2, pp. 255-278, 311-323, 1915, vol. 3, pp. 47-58, 1916. 13 Schreiner and Failyer, U. S. Dept. Agric. Bur. Soils, Bull. 31, 1906. <) 1911 j Ayres: Nutrient Solution on Plants Grown in Sand Cultures 307 500 c.c. had been used. The filter containing the sand was thru allowed to stand for about fifteen hours, and the sand was Leached with another 500 c.c. portion of water. The filtrate was evapor ated to dryness, the residue dehydrated at 100° C, and strongly ignited in a platinum dish to destroy organic matter. The resi- due was then dissolved in hot water and made up to definite volume from which aliquot portions were taken for analysis. A 2000 g. sample of the washed sand used in the experiment gave by this method the following analysis: N K P Mg Ca S 00. 33.6 5.2 06.4 2.4 15.6 milligrams In this analysis, as well as in all the following analyses, the statement made is for the total weight in milligrams of the element contained in 2000 g. of sand, which was the quantity contained in each pot. Table 4 gives a summary of the analysis of each of the sixty samples of sand used. The total quantity of each element present, calculated from the quantities of salts added plus the quantity in the original sand, is given, as well as the number of milligrams of the element missing from the pot at the end of the growing season. This latter value is the difference between the total weight of the elements present and the residue as shown by the analysis of the water extract. The difference thus obtained represents the quantity of the element absorbed by the plant and adsorbed by the sand particles. It must be admitted that it is not known just how great a factor adsorption may be in the case of this sand. Discussion of Results In series I no nitrogen as nitrate remained in pots 1, 2, 3, and 4 of groups A, B, and C. In group D there is a small residue of nitrogen in spite of the fact that the total crop production was greatest in this group. The concentration of the solution clearly affects the economical use of nitrogen, a fact which in general is also indicated in series II and in series III. It is especially noticeable that there is a much larger quantity of nitrogen left in series III D than in either series I D or II D. 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Hence in a solution where nitrogen is deficient, and potassium and phosphorus present in optimum amounts, a smaller crop production results than is the case where phosphorus is the deficient factor. A deficiency of potassium does not so seriously affect the intake of other salts, with the result that a better crop is produced than is the case where phosphorus is the deficient factor. The method of analysis which it was necessary to use makes the analytical values for phosphorus and magnesium rather un- reliable. In series II, where phosphate was added in increasing quantities from pot 1 to pot 5 in each group, the analysis of the water extract shows the effect of this increment. It will be noticed that the analytical values are all of about the same order of magnitude, winch may point strongly to adsorption by the sand. No general conclusion as to the adsorption of phos- phorus and of magnesium can be drawn for the reasons above enumerated. In the ease of potassium the method of analysis was much more accurate. There is evidence in series I, groups A, B, C, and D, of an increase in the amount of potassium absorbed which in general seems to be related to the more vigoi'ous growth re- sulting from the increasing quantities of nitrogen as added in these groups. A similar relation holds in the other two series, as will be seen from the ratios between potassium added and potassium remaining, which are higher where the nitrogen is added in large quantities than is the case where this element was present in small quantities. The high ratios of potassium added to potassium remaining after growth, therefore, usually occur where the dry weight is highest. Not much can be said on the absorption of calcium. In series I it is noticeable that the quantity of calcium remaining, as compared in the four groups of this series, bears an inverse relation to the calcium added. Less calcium is absorbed from the solutions of low total concentration than from those which have a high concentration. Since the crop production was 101 l!il7| Ayres: Nutrient Solution on Plants Gro Sand Cultures .'!71 greater in group I), the calcium must have been used with greater economy in this group where the total concentration was low. The Large aumber of variables which are presenl in each of the solutions make accurate deductions concerning the exact re- lation between any element and the growth of the plant almost impossible. In fact, growth lias been shown to be influenced i by one factor alone but by combinations of factors. GENERAL DISCUSSION It is evident, as noted above, that the large number of vari- ables present in an experiment of this diameter so complicates the situation thai definite conclusions are drawn only with con- siderable difficulty. Inorganic salts can be used by the plant only from solution. The complexity of this solution increases with the number of ions, which must be rather large since the plant cannot make normal growth unless certain ions are present. To further complicate the situation, all the salts may be avail- able which are required for growth, but the unbalanced condition of the solution may cause injury to the growing plant.34 This condition of balance, in turn, seems to be related to the total concentration of the solution as well as to its qualitative compo- sition. ;' In this connection it is important to note that if it were possible to keep the balance in the solution constant by renewal of salts, growth differences would be less marked than when the plant grows in a solution in which the balance is con- stantly changing due to absorption of ions by the plant.38 All of the above points must be taken into consideration in any ex- perimental work which is done in this field of investigation. The exact influence which the concentration of the solution lias upon the complicated physiological processes concerned in plant nutri- tion is a problem which can be solved only by the gradual ac- cumulation of a mass of evidence bearing upon the subject. The complexity of the whole problem is such as to require more than m Loeb, Archiv. ges. Physiol., vol. 88, pp. 68-78, 1902, and Airier. Jour. Physiol., vol. ::. pp. 327 338, 1900; Osterhout, Science, a. s.. vol. 35, pp. L12 L15, L912, and .lour. Biol, ('hem., vol. 1, p. 363, 1906. 35 > a 30 CO n < o > -< > PLATE 6 Treatment NaNOa Grams Ca(H»P04)o Grams K2so4 Grams MgS04 Grams Total Grams Pot IA4 2.0 1.2 2.4 .96 6.56 Pot IB4 2.0 .8 1.6 .64 5.04 Pot IC4 2.0 .6 1.2 .48 4.28 Pot ID4 2.0 .3 .0 .24 3.14 [376] z o "0 c 03 > o po CO O o PLATE 7 Treatment XnXO, Grams Ca(H2P04)o Grams KoSOj Grams MuS04 Grams Total Grams Pot IC1 .02 .6 1.2 .48 2.30 Pot 1D3 1.0 .3 .6 .24 2.14 Pot IB1 .02 .8 1.6 .04 3.06 Pot 1D4 2.0 .3 .6 .24 3.14 | 37* | « >l M co| o CO o en n < o "0 • PLATE 8 Treatment NaN03 Grams Ca(HoPO,)2 KoS04 Grams Grams MgSOj Grains Total Grams Pot 1IB1 2.25 .02 1.6 .64 4.51 Pot IIB2 2.25 .1 1.6 .64 4.59 Pot 1IB3 2.25 .2 1.6 .64 4.69 Pot IIB4 2.25 1.0 1.6 .64 5.49 Pot IIB5 2 12 5 2.0 1.6 .64 6.49 [380] o > ~0 03 o 'J, CO n o -■: IT LO l — i 0 I- >- Pl.ATE 9 Treatment NaNO., Grams Ca(H2P04)2 Grams K2SO, Grams MgS04 Grams Total Grams Pot EIA3 3.00 .2 2.4 .96 6.56 Pot IIB3 2.25 .2 1.6 .64 4.69 Pot IIC3 1.5 .2 1.2 .48 3.38 Pot IID3 .75 ,2 .6 .24 1.79 [382] o c: 03 33 CO n O PLATE 10 Treatment NaNOs Grams Ca(HoPO,)= KoSO, Grams Grams MgS04 Grams Total Grams Pot 11C1 1.5 .02 1.2 .48 3.20 Pot IIC3 1.5 .2 1.2 .48 3.38 Pot IIB1 2.25 .02 1.6 .64 4.51 Pot IIB4 2.25 1.0 1.6 .64 5.49 [384] o c CD CD C/5 n PLATE 11 Treatment NaN03 Grams Ca(H2P04)s Grams K.SOj Grams MgSO, Grams Total Grams Pot IB3 1.00 .8 1.6 .64 4.04 Pot IIB3 2.25 2 1.6 .64 4.69 Pot n ib:; 2.25 .8 2 .64 3.89 '386 J /. CALIF. PUBL. AGR. SCI. VOL. [AYRES] PLATE 12 Treatment NaKOs Grams Ca(H2PO.,),. Grams K2SO, Grams MgSO, Grams Total Grams Pot 1IID1 .75 .3 .02 .24 1.31 Pot IIID2 .75 .3 .1 .24 1.39 Pot IIID3 .75 .3 2 .24 1.49 Pot IIID4 .75 .3 1.0 .24 2.29 Pot IIID5 .75 .3 2.0 .24 3.29 f:;ss] n > (i I n "0 c 03 > CI -p CO O < o > ■< □ r" PLATE 14 Treatment Plant growing in washed sand Plant growing in soil NaN03 Ca(H2P04)2 KL.S04 MgSO., Total Grams Grams Grams Grams Grams Pot EIIB2 2.25 .8 .1 .64 3.79 [392] UNIV. CALIF. PUBL. AGR. SCI. VOL. I [AYRES] PLATE 14 PLATE 15 Treatment NaNO:! Grams Ca(H2P04)2 Grams K,SO, Grams MgSO, Grams Total Grams Pot ID2 .2 .3 .6 .24 1.34 Pot IID2 .75 .1 .6 .24 1.69 Pot IIID2 .75 .3 .1 .24 1.39 [394] UNIV. CALIF. PUBL. AGR. SCI. VOL. I [AYRES] PLA1