44 FLORIDA STATE HORTICULTURAL SOCIETY was deaerated under 28 indies vacuum and recovery of peel oil. By-products such as flash pasteurized at 190 to 200 degrees F., feeds, alcohol, molasses, etc. were not in cooled and filled into cans at a temperature cluded in the canning program. of 185 degrees F . C-enamel cans were used In conclusion it can be said that unfortu at first but later plain cans were used because nately Australia is in an unfavorable position the high acidity and high amounts of peel oil for her citrus industry due to the following in the* juice caused the enamel to peel off. reasons: (1) lack of efficient rail transporta One lot of grapefruit was tested just prior tion within her borders, (2) her home con to canning and the following results were sumption limited by the 6^ million popula obtained: Brix 12 degrees, acidity 3.8 per tion in an area almost as large as the U. S. cent, ratio 3.16 to 1; when sweetened with with little prospect of increased population sugar to a Brix of 15.5 degrees it had a ratio from heavy immigration, (3) restricted ex of 4.5 to 1 and it was too bitter to drink. An port trade as Australia is a long distance from analysis was made of some Washington Navel world markets and transportation to these oranges September 15, 1943, which is the lat would make the price to the consumer too ter part of the season, with the following high for competition, and (4) the high cost results: Brix 12.59 degrees, acidity 1.14 per of production per unit, with the attitude of cent, ratio 10.85 to 1, pulp of juice 12 percent the trade unions there making competitive and 75 gallons of juice per 2000 pounds of selling almost impractical. It can also be said fruit. Oranges analyzed from 30 to 50 mg. that some of the leaders of the industry and of ascorbic acid per 100 ml. of juice research workers are united in a movement Refuse or waste from citrus canning plants to better educate the grower to the applica was usually thrown away, except in a few tion of scientific work in an attempt to raise plants which converted orange waste into production and lower cost per unit through marmalades. A few plants had equipment for more efficient methods. This I hope succeeds. ROOT SYSTEMS OF VARIOUS CITRUS ROOTSTOCKS E. M. SAVAGE, WILLIAM C. COOPER and R. B. PIPER Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry, Soils and Agricultural Engineering, U. S. Dept. of Agriculture, Orlando INTRODUCTION darin, Morton citrange, Rusk citrange, sweet Fifteen species and varieties of citrus are lime, calamondin, and yuzu (kansu). This now being tested by this station for their value paper presents results of a study of the root as rootstocks for oranges, grapefruit, and systems of these various stocks. tangerines. These rootstocks include seedlings The rootstocks were grown in the nursery of the common sour orange, bittersweet at the experimental farm near Orlando. The orange, Pineapple sweet orange, Parson soil in this nursery is classed as Norfolk fine Brown sweet orange, rough lemon, Duncan sand. The seed were planted in January grapefruit, Bowen grapefruit, trifoliate or 1939, and transplanted to the rootstock nur ange, Cleopatra mandarin, Suen Kat man sery in November of the same year. The FLORIDA STATE HORTICULTURAL SOCIETY 45 plants were spaced 1 foot apart in rows 3 feet bearing trees. Al&o, as is obvious from the apart. They were budded with orange, grape photographs, the ends of many of the roots fruit, and tangerine varieties in May 1941. were clipped on excavation of the tree from The main rootstock plantings were planted the soil. It was almost impossible to obtain out at field spacing in 1942 and 1943. There every root of the plant intact. Accordingly, were, however, a number of the budded root- when a depth of 4 feet and a spread of 5 feet stocks left undisturbed in the original nur are observed in the photograph it is quite sery, and it was with these that the present possible that the actual depth and spread investigation on root systems was made. were slightly greater. The photographs show The root systems of the stocks were ex clearly whenever the roots were clipped and cavated and photographed in January 1945, the results can be interpreted accordingly. six years after planting the seed and nearly When taking the photographs, all plants four years after budding. Inasmuch as this were placed the same distance from 1Sie investigation is concerned primarily with the camera. A measuring stick marked in one comparative character of the root systems foot intervals was placed at the side and top of the various stocks rather than with pos of each plant. sible effects of the scion variety on the roots, Sour Orange (Citrus aurantium L.), Figs. tflie trees selected for study were all budded A 1 and A 2. to one scion variety, namely, Parson Brown This stock, which is widely used in Florida, orange. However, with one rootstock, the is frequently characterized as possessing Morton citrange, root systems of trees budded abundant and deeply penetrating roots. The to Duncan grapefruit and to Dancy tangerine photographs of this variety show three or were also excavated and photographed in more well-developed central tap roots pene order to determine with this one stock if there trating 3 to 4 feet deep in tihe soil. There were any striking scion effects on the char were numerous relatively small and delicate acter of the roots. lateral roots, particularly in the upper foot The stocks, having grown at close spacing of soil. Some of these had a horizontal for six years, had ttieir root systems fairly spread of 5 feet from the trunk to end of well mingled with the adjoining plants, and root. These laterals were well supplied with it was a slow, tedious task to extract the roots many fine, fibrous roots. intact. It was frequently necessary to uproot Bittersweet Orange (possibly sour orange several adjoining trees in order to remove hybrid, Swingle), Figs. B 1 and B 2. the entire root system of a desired plant. The root system of the bittersweet differed Because of these difficulties and because it mainly from that of the regular sour orange had been observed in digging the large num in having fewer laterals and very few fine ber of trees for field planting that the various fibrous roots. The central or tap roots were trees on any -one stock had remarkably uni more vigorous and penetrated slightly deeper form root systems, only two trees of each than the regular sour orange. stock were carefully excavated for detailed Sweet Orange (Citrus sinensis Osbeck study. It is believed that the photographs Figs. C 1, C2, Dl and D 2. shown are typical for these rootstocks under The root systems of both Pineapple and the conditions -of these experiments. Parson Brown sweet orange seedlings, which were very similar in character, showed well RESULTS AND DISCUSSION developed central roots, usually two, which In studying the results presented in figures penetrated the soil to about the same depth 1 to 17, inclusive, it should be kept in mind (3 to 4 feet), as the sour orange. There were that the trees under observation are young, numerous small lateral roots over the full and the depth of penetration and spread of length of the tap roots. The laterals in the the root system are considerably less than upper foot .were not so long as those of the that which undoubtedly occurs in mature sour orange. There was an abundance of 46 FLORIDA STATE HORTICULTURAL SOCIETY fibrous roots, particularly in the upper foot dwarfs the top of most varieties worked upon of soil. it. Its root system, with Parson Brown sweet These observations are not in agreement orange worked on it, was of fair vigor even with Mills' (1) observations that in California though- the growth of the top was dwarfed. the sweet orange has a shallow root system. It had deeply penetrating central roots and The results are more in agreement with numerous laterals with abundant fibrous roots Hume's (2) statement that the roots of sweet in the upper 1% feet of the soil. The root stock are equal in development to the deep- system was similar to that of the sour orange rooted sour orange stock. Oppenheimer (3), except it had a smaller spread of the laterals. likewise, reports that the sweet orange is Cleopatra or Ponki Mandarin (Citrus reticu- deep-rooted in the sandy soils of Palestine. lata Blanco), Figs. I 1 and 2. Rough Lemon (possibly lemon-citron hy The Cleopatra mandarin has received some brid, Webber), Figs. E 1 and E 2. attention as a possible substitute for rough This stock, which grows so well on the light lemon rootstock, on tiie assumption that it sandy soils of central Florida, had the most is more cold-resistant and produces better- vigorous root system of all fifteen stocks un quality fruit. It had a. cone-shaped root der test and appeared to be well adapted, by system with well developed central roots pene virtue of its root spread, for securing water trating vertically 4 feet or more into the soil. and nutrients from such soils. The stock was The long, fine-textured lateral roots in the characterized by its exceptionally large lateral upper 2 feet of soil were well supplied with roots which had a horizontal spread of 5 or fibrous roots.