RESISTANCE OF THE ROOTS OF SOME FRUIT SPECIES TO LOW TEMPERATURE A THESIS PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL OF CORNELL UNIVERSITY FOR THE DEGREE OF DOCTOR OF PHILOSOPHY \G. BY D. B> CARRICK it PUBLISHED AS CORNELL UNIVERSITY AGRICULTURAL EXPERIMENT STATION MEMOIR 36, JUNE 1920 SE mr pas Pe eo betes ¥ \x =~‘ CONTENTS PAGE neers ne MICEEALUEG sr, eek inl ek wales Cdicnee keke ee bee 613 frethud used im treezing the TOO... 2... 600.6265 2. eae ee G16 SSI EED Rios oie 0 ot ae re 618 Resistance of apple roots to low temperature.................. 618 Resistance of pear roots to low temperature................... 624 Resistance of Elberta peach roots to low temperature.......... 627 Comparative resistance of Mazzard and Mahaleb cherry roots to UTOE TeLen ESSE TE UT eee Ee Ow gee ee a 629 Resistance of Myrobalan plum roots to low temperature........ 632 Resistance of the roots of six grape varieties to low temperature. . 633 Resistance of blackberry, dewberry, and red raspberry roots to low ner Tube er vee Poe Se Le SEA UT ENT. eo ate 637 Resistance of gooseberry and currant roots to low temperature. . 63¢ Sap concentration of American and French apple seedlings and Wilder _ currant as measured by the freezing-point depression............ 642 Effect of rapid temperature fall on the freezing of apple roots....... 64¢ ‘Effect of rate of thawing on the freezing of roots.................. 645 Injury to apple roots when frozen in soil, in water, and in paraffin... 64¢ Influence of the scion on the hardiness of one-year roots of the stock. 646 Effect of sugar solutions, water, and drying out, on the resistance of pI OE HORTA eek eas Sn esas does he Vike a ONiK wake oe OS 653 SMMC APG aera me mee nes SPS a ty Se 5 gw oss gd anaeis a awdpe 656 ears ORCL ere era 8 Be rates tes che Dake kk aa ks Ve Cae SE 660 609 “x0 es at Fae siewsiale gle eee s ot toot 4 Ree Re ees ‘sunieteqmat wol of 2001 Tq seg 6 0-0, “non le ae Wa iY ote 4 soot yr laste bas inmsseaM to somsteiays & ta. iitlanalietiad wol a stook esuiley adaclowpe ll los iy as SOLS “pscitivcedato: wal of egifertay oderg zie to etoot oft t6 a wol of atoor "yniadqent bis bas cceecian ncrroddaglet toa ! a -guldarsqina} wol of 21004 farts bas vienna 70 2 Mb bas eguilbsse pave donot baa agsiysaré tot h RB Se Nes noigesicpob 1uod-BtiNegs? odd yt iouaaageeel it : 3BO... . . -Bloot olage to guiscort odt ao lel sinastoqengk: biget 6 : ty yes a GA > he Fee _, » -Btoer to gaisseTt adt ao getiwedY to stat Bok . “eae lit ban wataw ai lies ai assert aedw ator alga ¢ ; a cf aloota arly 20 aloo aoy-o00 to easnibrail oil? so-oise itt. Wy Se ei tb softsiaize: oly no suo adivtb bas-,totew (edtoliuios segnarie | Sete easy aes nee 4 re Weta nyc eet ee mini #00" fs Senn pe ares rere rae; : : ce Loads BOO ce « ee oe ee ee nye ag Ce cca aoe 4 z gee” | eo . ‘ aT : 7 a ay rs. — ie -a% Ae ~ re i - eA 7. a nS a Y RESISTANCE OF THE ROOTS OF SOME FRUIT SPECIES TO LOW TEMPERATURE (ee ae Ss Mae. “ag “Oni ine 40. eal AM ay wad io vie < ‘ 4 » ‘ i ’ Pied ¢ “ 4 ae, a é - ‘ \ ae * tt & » 4 Pare . ¥ t 7 RESISTANCE OF THE ROOTS OF SOME FRUIT SPECIES TO LOW TEMPERATURE! D. B. Carrick There are several types of winter injury to fruit plants which are of more or less frequent occurrence in New York State. Among these may be mentioned injury to small twigs, especially those of peach trees and of tender apple varieties such as Tompkins King; injury to the winter buds and sometimes to the blossoms; sun-seald, and the rather closely related forms of crotch injury and crown rot; and injury to the roots. Perhaps the killing of the roots by low temperature should be associated with the less serious types of winter injury in this State, due in part to the fact that it occurs in restricted areas. Yet in the Champlain Valley and in the upper Hudson River section, the freezing of the roots is one of the important problems in fruit production. This is also the case in parts of New England, in Canada, and in a number of the Western States. The work reported in this paper was begun in the fall of 1915 and: extended thru the spring of 1917. An attempt has been made to determine approximately under standard conditions the range of variation and the relative hardiness of some of the more commonly grown fruit stocks, including a few varieties of the small fruits. Some data were also obtained . regarding the influence of certain factors on the freezing to death of plant tissue. Careful field studies and the testing of possible fruit stocks capable of withstanding severe cold are significant aspects of the question that have not been attacked. It is hoped, however, that some of the results pre- sented here may be suggestive in the working out of these other phases of the problem of root injury by low temperature. REVIEW OF THE LITERATURE Craig (1900) observed extensive winter injury to the roots of apple, plum, and cherry in Iowa. The one- and two-year-old apple trees in the 1 Also presented to the Faculty of the Graduate School of Cornell University, in August, 1917, as a major thesis in partial fulfillment of the requirements for the degree of doctor of philosophy. AUTHOR’S ACKNOWLEDGMENTS. The author wishes to acknowledge his indebtedness to Professor W. H. Chandler for the direction of this work and for helpful criticisms given during its progress. 613 614 D. B. Carrick nursery were almost completely destroyed. In the orchard, apple trees from three to fifteen years old, situated on a north slope on light soils and unprotected by snow or vegetation, suffered very severely. It was noted, however, that hardy varieties rooted from the scion often withstood the same cold that killed trees which were wholly on seedling roots. The varieties least injured were: first, Siberian crab apple; second, native crab apples and the Hibernal type of Russian apples; and third, varieties of western origin such as Northwestern. The most resistant plum stock seemed to be Prunus Besseyz. No injury in any case was found in this species. Prunus americana was the next in resistance, being only slightly injured. Marianna roots were seriously damaged, while Peach and Myrobalan roots were entirely killed. The hardiest cherry root observed was the Morello stock, which, except where exposed, escaped with slight injury. Trees in the nursery on Mazzard stock were practically a total loss, while those on the Mahaleb stock suffered less. From the foregoing observations Craig concluded that the absence of snow or other protective covering during an unusually severe winter accounted for the very considerable root injury. To prevent a recurrence he advocated the use of desirable cover crops, the employment of the hardiest stocks available, and the deep planting of young trees, especially on the loess soils of the State. Emerson (1903) conducted an interesting experiment to determine the influence of mulching and soil moisture on the freezing of roots. He filled seven boxes, 2 feet square and 18 inches deep, with a loam soil, and planted twenty-five apple seedlings in each box. In the box protected by a 4-inch straw mulch, there was a soil moisture content of 16 per cent. By this treatment no roots were found dead and but seven were injured. In the box covered occasionally with snow and containing 15.8 per cent of moisture, seven roots were dead and eight were injured. Inthe unprotected boxes the injury seemed to vary inversely with the increased water content of the soil. With 10.4 per cent of moisture the roots of twenty trees were dead and five were uninjured; with 25.6 per cent of moisture, eight roots were dead, four were injured, and thirteen were uninjured. Not a root was injured in a box stored in a cool, dry place, altho its soil contained only 10 per cent of moisture. REsISTANCE OF Roots or FRuItT SPEcIES TO Low TEMPERATURE 615 Emerson (1906) found some striking differences in the protection of certain cover crops against deep freezing. In one case in which the snow was held, the ground froze to a depth of six inches where corn was planted, twelve inches with a heavy cover of oats, fifteen inches under a medium heavy crop of millet, and twenty-four inches where the soil was bare. These facts suggest. the use of cover crops which will catch and hold the snow in regions where root injury is prevalent. Macoun (1908) mentions the killing of roots as one of the ten forms of winter injury occurring in Canada. He recommends the use of cover crops as a means of increasing the soil moisture and holding the snow. His observations on the effect of soil moisture were similar to the expe- rience of Emerson. He states also that the grafting of apples on the garden crab-apple trees has somewhat reduced the root injuries due to freezing. By means of careful artificial freezings, Chandler (1913) obtained a considerable amount of interesting data on the relative hardiness of various fruit stocks. He found that the range of killing temperature of apple, peach, pear, and plum roots was from —3° C. in summer to —12° in late winter with rather rapid freezing. He compared the killing tempera- ture of apple roots actively growing in the greenhouse with that of dormant ones in cold storage, in basement storage, and outside in frozen soil, respectively. The three dormant treatments showed little difference in resistance, but the active tissues killed at three centigrade degrees higher than did the dormant roots. Similar comparisons of peach and Marianna plum roots showed somewhat less variation between the conditions of growth and dormancy. Chandler observed also a diminished hardiness in the roots farthest from the crown, apparently varying with their soil depth. He demon- strated further that in most cases the roots coming from the scions of Ben Davis apple trees were hardier than similar roots from French apple seedlings. An extended laboratory determination of the comparative resistance of Marianna and Myrobalan plum roots and Mahaleb and Mazzard cherry stocks strongly confirmed Craig’s observations under orchard conditions. Mix (1916), while studying sun-scald in the northern part of the Cham- plain Valley, New York, observed a great amount of winter injury in the roots of apple trees from one to twenty years old. The injured condition 616 D. B. Carrick seemed most serious where fall plowing was practiced and where the trees were on light soils and in windy situations. The Ben Davis trees were especially susceptible, from 50 to 75 per cent of these being left in a dying condition. Northern Spy and Wealthy trees also were injured, but in a degree much less than the Ben Davis. Mix observed also some cases in which, as he states, “‘ the hardiness of the stock seems to have been influenced by the scion.” METHOD USED IN FREEZING THE ROOTS The apparatus used in this study for freezing the roots consisted of: an inner chamber of galvanized iron 9 inches long, 14 inches wide, and 30 inches deep; an outer chamber of the same material, 6 inches long, 12 inches wide, and of the same depth as the inner chamber; and around the outer chamber, 5 inches of insulation held in place by a casing of wood. The roots to be frozen were placed in the inner compartment, and were surrounded by the freezing mixture of ice and common salt in the second chamber. At no time was the actual tissue temperature determined, but the temperature of the air around the tissues was measured by means of three electrical resistance thermometers and a balance indicator. The latter instrument consisted of the circuit of a Wheatstone bridge mounted in a suitable case with a galvanometer and means for balancing the bridge by moving a contact along a slide wire.2 The three electrical resistance bulbs, each with leads 5 feet long, were used until the variation in temper- ature in the lower part of the freezing chamber was determined. These bulbs were standardized by the makers and were carefully checked against one another in the laboratory here. The bulbs were securely attached to a piece of hardware cloth 6 inches square. The various roots to be tested were fastened to this wire by means of rubber bands. The bulbs always stood perpendicular to the bottom of the chamber, and the roots were always arranged on the cloth parallel to the bulbs. Careful tests showed that, while the temperature was uniform at given levels within certain limits, it varied slightly at different levels. Because of this fact, a complete record as to the injury in the lower and in the upper ends of the roots was kept. To further standardize this variation, all of the pieces of material used were cut 4 inches in length. When the 2 This is a standard apparatus obtainable from the Leeds, Northrup Company, of Philadelphia, RESISTANCE OF Roots oF Fruit SpeEciEsS TO Low TEMPERATURE 617 hardware cloth and the bulbs were in position, the roots extended to within one inch of the bottom of the chamber in a regular row. The difference in temperature on either side of a bulb — that is, hori- zontally — within a compass of five inches was found to be negligible. However, a number of tests of the temperature in either extreme end of the freezing chamber showed that a maximum difference of one centigrade degree might exist. Accordingly, no roots were tested at these points. In order to subject all the material to as nearly uniform conditions of freezing as were possible, the killing temperature of a number of different roots was determined at the same time rather than an attempt being made to freeze at once many roots of a single sort. Owing to the variety of roots used, however, it was neither practicable nor desirable to test all of these at any onetime. As they naturally divided themselves into groups of more or less tenderness, material of similar resistance was usually frozen together. While the temperature was being gradually lowered, the inner compart- ment was kept tightly closed. In no case were any of the roots removed before the minimum degree was reached. Since several workers have found a distinct influence in the amount of injury resulting from the rapidity of cooling, care was taken to allow a standard rate of fall for all freezings, except as noted to the contrary. This uniform lowering of temperature began at 1.5° C., and reached O° in fifteen minutes. The fall from this point to the desired degree was at the rate of one degree every twenty-two and one-half minutes. The minimum temperature was always maintained for fifteen minutes. Ordinarily the roots were removed from the chamber and allowed to thaw rapidly. Russell (1914) and others have noted that the death of a plant from freezing is rarely immediate but may be delayed for several days. Because of this possibility the treated roots were set aside and examined at different intervals. During this time they were kept moist by placing them on a hardware cloth which projected above the surface of the water in an agate pan. The roots and the pan were covered with a bell jar. An inspection of the roots for injury was usually made within from one to three days after exposure. In most cases when injury occurred, it was apparent by the end of this period. At first microtome sections were prepared and the character of the injury was determined with a low- 618 D. B. Carrick power microscope. This was soon found to be unnecessary, since the color changes of the frozen cells, except in the gooseberry and the currant, were rather striking. The affected tissues of the apple became of some shade of brown and appeared water-soaked; in Mazzard cherry, Myrobalan plum, and red raspberry roots, the injured cells were somewhat yellowish; while in the blackberry and the dewberry they often appeared almost black. The early appearance of Rhizopus species and probably other saprophytic fungi on the dead part was also characteristic of injury. In not.an instance did the fungus or the discoloration appear in the unfrozen roots left similarly located for comparison. The roots of all species tested from October 24 to November 18 were collected from the nursery row. All the leaves were present on the plants used. in the first determinations and some had not fallen in the latter freezings.. The remainder of the material was kept in common storage and removed as needed. With this material the temperature varied somewhat, due to outside changes, but it seldom went. below 0° C. and did not-rise above 5° until April 1. The plants were stored in normally moist sawdust, and there was little opportunity for them to dry out later as they were placed on the hardware cloth attached to the resistance bulb while in storage and were then immediately frozen. RESULTS OF THE EXPERIMENTS RESISTANCE OF APPLE ROOTS TO LOW TEMPERATURE Yor all the tests conducted, the diameter of each end and of the center of the root, and the date of freezing, are recorded as possible factors that might influence the kind or the amount of injury. The results of the tests with apple roots are shown in table 1. Four kinds of seedlings were used: one-year American stocks, grown in this country but from French seed; one-year French seedlings imported from France; two-year French roots which had grown for one year in the nursery here; and one-year stored French seedlings which had been held at approximately 0° C. in cold storage for one year. One noticeable feature in the apple freezings was the differences in the individual resistance of roots similarly treated and frozen apparently under the same conditions. Unless the temperature is above or below the average freezing point, all gradations of injury may occur. RESISTANCE OF Roots oF Fruit Species TO Low TEMPERATURE 619 TABLE 1. Temper- ature Date of (centi- freezing grade) —7° | October 24 to November 18 — 9° —9° —9° | December to January —10° —12° —9° | February to March Variety American 2-year French American 2-year French American 2-year French American 2-year French 2-year French 2-year French American 2-year French Errect oF Low TEMPERATURE ON Roots oF APPLE SEEDLINGS Diam- Num= Per cent of cells killed eter Num- | ber of in injured roots of roots | ber of roots (milli- | roots unin= Gants meters) jured Pecans Phloém |Cortex 7x6 2 PANT Cee tac hte aa Ke del (va 5x4 4 3 50 50 50 4x3 (| le Cee 40 40 40 (x0 10 OF ears ces dls ME etre Bk 5x4 8 5 40 40 40 4x3 GH eatesace: 60 50 50 5x4 1 oe eee eee ence wid coke 4x3 8 2 40 20 20 Sac i) en Pa aie 50 50 50 LEO Seal |S Seto neal [ak Cees teas ew dee 5x4 Dy) Mp lek, Sieg S| | RNR (ee Sa 4x3 13 2 60 60 60 i Xao 3 I 35 35 35 6x5 I aot CS 25 25 50 5x4 4 1 90 90 90 US) 2 THE NS AR arn bee, ee Boe | |S PE 5x4 OnlPaencs 75 75 75 4x3 5 Oe Mae See (LAR: ge [pee 9x7 5 2D 80 35 35 6x6 4 | 50 45 45 5x4 ae ee 75 60 60 exo 6 4 5 5 10 Hes 6 2, 35 20 20 4x2 6 3 80 65 65 exe 5 45 15 15 F528} 14 | 50 50 50 4x3 1 gst | eR 60 60 60 8x6 Dae o 5 5 5 4x3 P| leer aaa 100 100 100 7x6 9 6 20 10 10 5x4 9 4 60 60 60 8x5 3 51s (Cae rer | | Sc aeeeeieam ee Cran Ser i, ae ee 50 620 D. B. Carrick TABLE 1 (continued) — —= T Diam- Num= Per cent of cells killed eas bate gh eter Num-: | ber of in injured roots é ae f a s Variety | of roots| ber of me , ee (milli- | roots grade meters) —10° | February | American 7x6 12 to 5x4 8 March 3x2 10 Oi a a 2-year 7x5 3 French 3x2 8 =—112 American 7x6 12 5x4 6 3x2 30 2-year 6x5 5 French 3x2 20 1-year 8x5 5 French Sexe 8 —12° American 7x6 9 Hx & iil 4x3 8 Shae 2p) 2-year 6x5 5 French Syne 2 33 1-year 8x6 + French Oke 19 1-year 8x5 4 French, exer 22 stored =e L-year 8x6 4 French 190 American 7x6 8 3x2 16 1-year 3x2 9 French, stored — | _ ] | |] SF —14.5° American 7x6 15 3 RESISTANCE OF Roots oF FrRuItT SPECIES TO Low TEMPERATURE 621 —10° = —12° Date of freezing February to March (concluded) March 29 to April 15 TABLE 1 (continued) Num- ber of roots Per cent of cells killed in injured roots SE ee ee eed Diam- eter Variety | of roots (milli- meters) l-year Sal French ox 2 | | | | ——_—_——_ __ ] —_———_ 1-year 8 French 6 60 =e © aie alae i's o-5 o © ea sf « «= =, © eee ee eed American 8x6 6x4 es ee i | | | | | 1-year 8x6 French, stored S| | | | | 1-year 8x6 French 6x4 100 45 60 | | | | | American 8x6 | | | | 1-year 8x6 French, stored 100 100 | | | | | 1-year 8 French 3 100 —————— | | | American 75 100 a ——— | | | | | l-year 8x6 French, stored 100 ee es ee ee l-year 8 French 3 100 100 100 100 ee ee en ed American 15 l-year 8x6 French, stored 100 100 100 100 - | ——— | + |] | — —— —— —_ ] —_—__——______ | -_ 622 D. B. Carrick TABLE 1 (concluded) } Te mM Diam- Num= Per cent of cells killed pee Daisd eter Num- | ber of in injured roots (ent reer Variety | of roots| ber of roots aie) & (milli- roots unin-= Cat 8 meters) jured bi Phloém |Cortex ium —/ April 16 1-year 8x6 2 Zit ss eke hee. Al ee to French 3x2 ule sagen 50 50 50 May 8 American 8x6 7 | 100 100 90 6x4 a ee S| eae ae ee |B ad 1-year axoO 2 2 clicccke. pB ped eashhore i eee French,| 3x2 4 Aull sf soe Alen Secs | See stored —8° l-year G6 4 7 ae (rns |e - French, See 2 13 4 80 25 25 stored American 8x6 4 1 80 25 25 6x4 Baby. 22 ate 90 80 80 1-year 8x6 Poa) ieee ase LOW ao. Sa eee French,| 6x5 a ae 90 90 90 stored —9° 1-year 8x6 2 2 shoo geo here oe ee French Exe 7 7 fa Pe el Re Ss = American 8x6 6 3 25 |... 254. 0e eee l-year 7x4 2 PH Ed cary iil ty loti 3 French, Shoe AL ie ied sea 100 100 100 stored he American 8x6 (el eases aa 70 60 60 6x5 Gil Keats ee 100 100 100 It is a common opinion among some nurserymen that the French- grown apple stocks are hardier than the home-grown seedlings. The results obtained from the freezing of hundreds of roots of each stock indicate that these differences in resistance are negligible. Both stocks are found to show considerable injury from —11° to -11.5° C., and at -12° few of either sort survived. The two-year French roots were grown RESISTANCE OF Roots or Fruit SPECIES TO Low TEMPERATURE 623 under unfavorable conditions in the nursery, and apparently because of this were more easily killed than the one-year stock. The one-year seedlings held in cold storage for one year showed about the same hardiness as the two-year roots. The observations of Chandler (1913) led him to conclude that the hardiness of the root tissues varies with the season. This is to be expected and the results obtained readily support this theory. The material frozen in October and November shows a marked tenderness compared with roots tested in February and March. The period of maximum resistance seems to end somewhat before the last of March, tho the date would, of course, vary with the conditions affecting after-ripening and possibly also with the variety. From the first of April until these observations ceased, an increasing amount of injury was noted. This range of hardiness indicates a difference in resistance of between three and four centigrade degrees. These seasonal differences obtain, not only in the apple seedlings, but in all the roots reported in this paper. The influence of the size of the root in withstanding cold seems reasonably well established by the data in table 1 as well as by those in the succeeding tables. The resistance is in direct proportion to the diameter of the root. In practically all cases in which the whole forked roots of the French seedling were employed, the small roots killed first. Similarly, the smaller roots of the American stocks having the same soil depth suffered more quickly and severely than the larger roots. The results in the apple tests seem to point rather clearly to the relative resistance of the different tissues in these roots. It is seen, in practically all instances in which injury occurs, that the cambium is the first tissue to be killed. This is followed closely by the phloém, while the cortex seems somewhat hardier than either of the other tissues. Only a few cases are recorded in which the cortex alone was severely injured, tho frequently the three tissues were equally affected. Unless the temperature is especially low for apple roots, or they are especially tender as in the fall and the spring, the cambium, the phloém, and the cortex are browned without further injury. Occasionally under extreme conditions the xylem and the pith may be killed, in which case they both seem to show about equal resistance. An exposure at —20° C. would ordinarily kill all the cells in the roots of any apple seedlings tested in these experiments, even when they were in a dormant condition. 624 D. B. Carrick A number of observations were made on material four inches long, in which two inches of the plant represented the stem above the soil level and two inches represented the root below the surface of the ground. From the results of these freezings some indications were given as to just where the tenderness of the root tissues ended and the we!l-known hardiness of the stem tissues began. Where injury occurred to the specimen, the region of browning much oftener than otherwise extended from the lower end of the root upward, decreasing abruptly at the crown. This is some- where near the point of differentiation of root and stem structures. It was indicated from these data that this difference in resistance may have been brought about by a change in cellular structure. While Chandler (1913) seemed to find that roots deeper down in the soil were tenderer than those near the surface, an examination of his data shows that the deeper roots were also considerably the smaller in diameter. Many observations of roots of equal transverse section and growing at different soil levels were recorded from time to time. From the results of these observations, it was suggested that the size of the root was, perhaps, a greater factor in its resistance than the soil depth at which it grew. From the foregoing considerations it is rather difficult to assign a fixed temperature at which an apple-seedling root may be partially or completely injured by freezing. Examination of all of the material tested showed that, while severe injury is found at exposures ranging from —7° to —13° C., one French root survived a temperature of -14.5°. However, the majority of the dormant roots were seriously injured in the three outer tissues by a temperature of —12° C. RESISTANCE OF PEAR ROOTS TO LOW TEMPERATURE In the work with pear roots the comparative tenderness of two-year French stock (Pyrus communis) and one-year Kieffer stock was determined. The two-year roots were given the same field treatment the second year as was given to the two-year French apples previously mentioned. A few one-year French stocks were also available in 1916. In almost all cases, as shown by the data recorded in table 2, the one- year Kieffer roots proved more resistant than either of the French stocks. At an exposure of —10° C. in the January-March period, the Kieffer roots show a less number and percentage affected than do the two-year French REsISTANCE OF Roots or Fruit SpEctEs TO Low TEMPERATURE 625 roots. survival of either species. again demonstrates its superiority. When exposed to —9° in April the Kieffer shows only a small amount of injury in the phloém while the two-year French roots were killed thruout. The temperature of —11° during dormancy was too low for the In the April tests at -8° the Kieffer stock TABLE 2. Errsect or Low TEMPERATURE ON Roots oF PEAR SEEDLINGS Temper- ature (centi- grade) —=10° eid —12° Date of freezing to December 15 January to March Diam- Nume | Per cent of cells killed eter Num- | ber of in injured roots Variety | of roots| ber of | roots (milli- roots unin= Gan meters) jured bane Phloém |Cortex 7x6 8 6 ZOE ers Mok S| Neo French 4x3 br, | leapt 100 100 100 8x6 10 2 do 75 75 5x3 say | eae 100 100 100 WEXcO 3 | 50 50 50 ko (c) | ere 100 100 100 9x8 3 | eee 60 60 69 4x3 Ghee es cat: 100 100 100 2-year 8x6 5 4 100 100 100 French oxo tobe | fa, Se apeieheor 100 100 100 9x7 4 1 100 100 100 5x4 113} 3 etna Shs 100 100 100 1-year 6x6 6 3 60 40 40 Kieffer 2-year 9x7 5 | 80 85 85 French 6x4 (iol near es 85 80 80 l-year 7x6 (|| etl 100 100 100 Kieffer 2-year 7x6 AA Rre en hee 100 100 100 French 1-year 8x7 Pde || 4 bel Sema 100 100 100 Kieffer (x Di ie aA yon 10 45 45 2-year 8x6 2 2 es aR Es] tae a el (to French 4x3 4 3 50 50 50 7 626 D. B. Carrick TABLE 2 (concluded) Temper- Diam- Per cent of cells killed See Date of eter Num- in injured roots (centi- iccaea Variety | of roots} ber of rade . (milli- | roots & meters) —7° April 1-year 6x6 3 (conc.) 1 to 21 Kieffer 6x3 3 ————| (concluded) ees) Sees) PEs een Se ee — he 2-year 8x5 3 French l-year 6x6 9 Kieffer 1-year 6x6 2 French 5x4 12 4x3 8 —9° 2-year 7x5 3) French l-year @x5d 3 Kieffer 1-year 6x4 9 French Sa a —10° 2-year 10x6 3 French 1-year 7x6 3 Kieffer l-year 8x5 3 French The pear roots, like those of the apple, showed individual variations — an increase in hardiness with an increase in diameter, a region at the crown less tender than the root below, little influence due to depth below the soil surface, relative tenderness of the same tissues, and a gradual acquiring of hardiness thru the winter, reaching the maximum in February and March. This seasonal hardiness, however, seems rather more delayed in the pear root than in the apple. RE&sISTANCE OF Roots oF Fruit Species TO Low TEMPERATURE 627 If the resistance of the pear and the apple seedlings is contrasted, it is found that an approximate difference of from one to two degrees generally obtains, and sometimes even a much greater difference. Thus, while in March the apple does not begin to show much injury until a temperature of —11° or -12° C. is reached, -10° or —11° is sufficient to kill most of the tissues, except the xylem and the pith, in both the French and the Kieffer pear stocks. RESISTANCE OF ELBERTA PEACH ROOTS TO LOW TEMPERATURE The name Elberta as used here refers only to the bearing surface of the tree and has no reference to the origin of the roots. The peach stocks probably were derived from several different varieties; at least, the range of variation presented in table 3 indicates such a possibility. TABLE 3. Errect oF Low TEMPERATURE ON Roots OF ELBERTA Pracu TREES Diam- Num= Per cent of cells killed in Temper- eter Num- | ber of injured roots une Date of of roots | ber of | roots (centi- freezing (milli- roots unin= grade) meters) jured | Cam- | phlosm | Cortex | Pith bium —8.5° | February 12 12x6 2 PTB ers BPs 6s] | EY che Pee Se ccs Ore to 5x4 Nee eae S| ee geek IO ace VD |Rese os March 24 —10° 15x8 Sa |eeeeen ee 100 100 100 100 10x6 6 2 90 90 90 60 C5 Dilek Fee 100 100 100 55 5x4 Cleese coe 65 65 65 45 —11° 15x8 ie oe 100 100 LOO eee: 10x9 Or eee ee 30 30 35 45 Gx5 4 24 |e oon eee Baie ee 100 5x4 COA ee hie, aot 35 35 35 100 —12° 12x8 ON ae ae 60 60 60 100 10 x6 Sil eae ae Re 40 40 40 100 Oxo DE CR ee eee 40 100 4x3 As igure. 7x8 | | ain en BOW avetesereresots 25) (ll hele aera Besseyi| 7x6 Ais esse eae LOOM Sactrste sis 30 LOOM aera —15° Mahaleb | 10x8 Heal shcete eS 20 20 20). 3h ale eee 7x6 2 1 30 30 30". Soke lee Mazzard | 10x8 Aap betas ee 100 100 VOO! | o.<:.8 opal S| |e | —_ | - —_ ] ——_ ] —_——_ ] _-——_ Prunus 7p >< [6 > yal ee ee 100 100 100), :c.clasiteeeee Besseyi —17° Mahaleb 8x7 B.A Teena 75 me 75 )| pee onleeeeee Mazzard 8x7 Zl Grcreniars 100 100 100 LOOA Set ae Prunus 9x7 Te ees Crees ae 100 100 100 100 50 Besseyi —7° Marah 30 Mahaleb 9x4 2 DPN Sor cave BI ace ar nieder ell altos ocvesai| Pence Seereng | eee oO eee SS Oe ee April 20 Mazzard 9x8 7 Wa eer oe eS 100 100 TOO 3):3,<2 ngs cle —8s° Mahaleb 8x5 4 Ah ctewidl joan alee ote eee ee Mazzard | 12x11 2 1 40 40 AON scorn io eee 8x6 Da Neier ae ee 100 100 100°... Slee eee =!) Mahaleb 9x5 2 Diil's oe z-cce|laseaetiete elites ie cee tere See ee 8x3 19) 4 15 15 156). a4 wttyve3 Ree Mazzard | 10x8 By Mncpatonn ans’ 100 100 ROOM sc cate sltepeeerae 8x5 yg lee ee ee a 100 100 TOO! Oc eee —10° Mahaleb 7x6 5 Bel bs Suntec Se ailllves! nc el| Sites ae eee 5x 2 P| Tees eh 40 40 AO) | 2% stool bone Mazzard | 10x9 (ee Wah Sets) oes 100 100 LOO 3) kis toe hee 8x8 CS rere ee 100 100 100 100 50 ——11° Mahaleb 8x4 2 Dee cali alba apace ave raral iat Gee eal eal. ee | eee Mazzard 8x8 Sule bens ce 100 100 100 LOO) | ceerete —12° Mahaleb 9x6 dia eens SIS Ae oy, 60 75 UDA ahe bie tae | heme 7x4 Bi) etoneheece DO Glitecrereieroe DOM rereveh alo eae Mazzard 12x10 Bi || ae eee — 100 100 100 OO clever 8x7 Moll Saves Oe 100 100 100 100 100 7x4 SB lacretea te 100 100 100 100 100 RESISTANCE OF Roots or Fruit Spectres TO Low TEMPERATURE 631 The most striking fact brought out by the data in table 4 is the uniform tenderness of the Mazzard as compared with the Mahaleb stock. This difference can readily be seen in any comparable instance. It extends thru all stages of maturity. Thus, during November, Mazzard tissue was injured much more severely when exposed to -8° C. than was cor- responding Mahaleb stock tested at -9°. In the January-March period a similar difference is noted; the six larger Mazzard stocks given an exposure at -11° show 85 per cent browning in the three outer tissues, while three smaller Mahaleb roots were similarly affected only 10 per cent when exposed at -12°. At -15° the Mahaleb tissue suffers relatively little injury, but the two roots subjected to -17° are mostly killed. In the March-April period the continued resistance of the Mahaleb tissue is striking. On April 15 it is about three or four degrees hardier than the Mazzard, which when exposed to -10° is seriously injured in the pith and the xylem. These results are in accord with the field observations of Craig (1900) and the laboratory studies of Chandler (1913). The freezing tests with Prunus Besseyi, altho this is a plum species, are included in the cherry data since it is frequently used as a cherry stock. These results with Prunus Besseyi do not bear out the experience of most writers regarding its exceptional hardiness. During the January-March exposures, it is noted that at -11° C. this variety was injured somewhat ‘more than was the Mazzard. At —12° it was rather more resistant than the Mazzard but the pith in the smaller roots was killed thruout. At —15° and -17° it suffered equally with the Mazzard or worse. Under field conditions with severe freezing, Craig (1900) found Prunus Besseyi much hardier than all other stocks used for cherries. The writer is not prepared to say that the hardiness of this species has been over- estimated. His own very limited experience, however, shows it to be inferior in resistance to Mahaleb, and slightly better than Mazzard. Since the writer is not familiar with the Prunus Besseyz stock, it is of course possible that the roots tested as recorded above were not of this species. The only evidence that they were correctly named is from the nurseryman who sold them as such. A small amount of data on Prunus avium and Prunus pennsylvanicum, not included in table 4, indicate merely that these roots seem to be quite as easily killed by freezing as are Mazzard roots. Since these roots were taken directly from the partly frozen ground in April, they were rather 632 D. B. Carrick moist and were probably beginning activity. A larger number of deter- minations under different conditions might entirely change the tendency just mentioned. Considering the data on the four cherry stocks, their order of relative | hardiness seems about as follows: Mahaleb, Prunus Besseyi, Prunus pennsyluanicum, Mazzard. If the Mahaleb cherry is compared with the apple, it is seen that the resistance of the former is markedly superior in most cases. In large Mahaleb roots during their hardiest period, little injury is found under —14° C., while at -15° the injury is relatively small. Prunus Besseyi did not survive a temperature of -11°. Prunus pennsylvanicum succumbed at -10° or -11°, altho the date of freezing may partly account for its tenderness. The Mazzard roots in no instance withstood -11°, but the number of tests run at —10° was insufficient to place this as its minimum. From these results the Mazzard cherry stock does not appear hardier than Kieffer pear stock. RESISTANCE OF MYROBALAN PLUM ROOTS TO LOW TEMPERATURE Unfortunately, only one commonly used plum stock was available in this work, aside from the Prunus Bessey roots included in table 4 with the cherry stocks. The number of one-year Myrobalan roots tested was too small to give very conclusive results. However, some indication at least of its comparative hardiness may be gained from table 5. The data in this table place the one-year Myrobalan root in the same group in regard to hardiness as the pear and the Mazzard cherry. The Myrobalan plum does not appear quite so hardy as the Kieffer pear and probably it would prove to be less hardy than a vigorous one-year French pear. The fact that the roots of the latter are normally somewhat larger than the average plum roots, would give still more evidence in favor of the superior hardiness of the pear. REsIsTANCE oF Roots or Fruit Species TO Low TEMPERATURE 633 TABLE 5. Errect or Low TEMPERATURE ON MyropaLan Pium Roots , Diam- Per cent of cells killed veer D f eter Num- | Number in injured roots ature ate o of roots | ber of | of roots Sapa freezing (milli- roots | uninjured grade) meters) —7° October 24 8x7 hi | eels nee tae to was Lal Boa ane te December 20 —s° 5x4 sa | Lat aoa S a aa —9° SED 3 1 Oxo PAs VE Mey 2 erate —10° 9x5 A alae Pe aes 8x7 DRIES dak oe 3 —9° January 1 7x6 Gide tae Une to 5x4 le ete. 52 March 29 yi dik thi Lal Nebaaieeee aes —10° 8x5 Deis, 2. ee 5x4 OU erst. Aree —11° 9x7 DR eal Rar te 5x4 Ae secon —s° April 1 to 8 6x5 BU eo tae 5x4 7 ( made a es ~ ~ zd a - wre iaaid 998888 ran ry Tian / ot a fal Aa, rrr nnn / 4 WES 4 Gas / 4 WT hanna + the differences in etter case were always very small and were prodably ranked ‘te inherent variation. Om examination of the previous te Mareh 17 (table @), the Baits of this Bander group aie appar 636 D. B. Carrick ent. Only seattering injury is recorded at —11°, -12°, and -13°C. Atan exposure of —14.5°, twenty-two out of twenty-seven Concord roots were uninjured and only a trace of cambium and cortex injury was noted in the remainder. One-half of the Clinton and two-thirds of the Diamond roots were injured more than 50 per cent by the same temperature. At —15.5° an injury of 20 per cent is seen in one-third of the Concord roots and 15 per cent more in the other two varieties. At —18°, however, the cambium, phloém, and cortex tissues were completely injured in all roots, with some xylem injury in the Diamond and the Concord. By March 21 tender- ness began to return, and a few days later these varieties were severely injured by temperatures several degrees higher. A contrast of the root resistance in the varieties of the second class shows the following order of hardiness: Norton, Lindley, Cynthiana. The variations, however, are so slight that they may be entirely disregarded. In 1917 Cynthiana was quite as resistant as Norton, as shown by the injury in both at the higher and lower temperatures. Lindley seemed to be a trifle easier to kill than either Cynthiana or Norton in 1916, but here again the differences are slight. The limits of this second group as shown in table 6 lie between -—10° and -12° C., the roots usually undergoing considerable injury at —11°. In relative hardiness this places these varieties between the Mazzard cherry and the apple. The Clinton, Concord, and Diamond roots, even excluding the influence of size, are considerably more resistant than apple roots, and Concord and Clinton seem equal if not superior to the Mahaleb stock. The results shown on comparing the hardiness of the respective species of grapes are somewhat as would be expected. Vvtis aestivalis, represented by Norton and Cynthiana, is not adapted to severe cold, and this may account for the fact that its range is limited to the South. The tenderness of Lindley is probably due in part to the influence of Vitis vinifera, which, as is well known, will not survive the winter in the latitude of New York State without much protection. Concord and Diamond represent Vitis lebrusca, the Northern Fox grape, which, while restricted in distribution, is found in Maine. Vitis vulpina, represented by Clinton —a variety with extremely resistant roots — has the greatest range of any American species of grape, it having been found in Canada north of Quebec. RESISTANCE OF Roots oF FRUIT SPECIES TO LOW TEMPERATURE 637 RESISTANCE OF BLACKBERRY, DEWBERRY, AND RED RASPBERRY ROOTS TO LOW TEMPERATURE An attempt was made to test representative varieties of blackberries, dewberries, and red raspberries, in order to determine any varietal or specific differences in the hardiness of their roots. But, since many of the roots either were dead when received or blackened soon afterward, little variation among varieties is recorded. Only one-year plants were used. Since the one-year roots of the black raspberry are so small, and injury to them is difficult to detect, no data are given on this species. Comparison of the resistance of the blackberry varieties recorded in table 7 shows the Eldorado to be apparently the least affected. The roots of the Early Harvest and the Watt show about equal tenderness. TABLE 7. Errecr | oF Low TEMPERATURE ON THE Roots oF BLACKBERRY, DEWBERRY, AND RED RASPBERRY T Diam- Num- Per cent of cells killed in injured eee Tate-of eter |Num-| ber of roots Give | Pstgct | vasioty | otranie| berf| room | milli- | r - grade) meters) jured a Phloém |Cortex| Pith |Xylem —9° March 6 Eldorado 5x4 5 Doe |e ne evaten sll Semel acc oll chars Gere to 20 Watt 5x4 5 1 50 50 7.0 Se eee ches call (eter eey cn Early 6x5 2 PAGS 6.5. taco | penance kee Dieh (Ptencue eed lesiae aes] Leia aioe Harvest 5x4 Siete sce 45 45 royal eae pd eso Oe Lucretia 4x3 5 Bribie acces ores eS obeheve s Nevapaeermelaretet aces Austin 5x4 5 2 85 85 SH eyeeene |: sites —10° Eldorado 3x2 10 MO arch We le ort: dete raretat nil ceeds move betets ieee 5 Watt 3x2 Tight (iekctene Soc: 60 60 60 cH 0 Wil eseeees Ae Early Harvest ax 11 9 50 50 50 50 Lucretia 3x2 10 9 25 25 7a ae Seis) (aeeiee oat Austin ox 2 10 9 25 25 DIN ate eet varalare —11° Eldorado 5x4 6 4 15 15 i144 ee eae (oe ae Watt 5x4 7 5 100 100 100 SOK | ares Early Harvest 5x4 6 5 100 100 MOO a Scrcta alata steyous Lucretia 5x4 5 4 50 50 DO Eye ose tilaeoets SD 8 3 100 100 OO RR ee tee —12° Eldorado 6x5 1170 I 100 100 100 0) era Watt 6x5 tO eT ae ees 100 100 100 20 Early Harvest 5x5 VE chetatinxe 2 100 100 100 BOL eee Lucretia 5x4 8 1 75 75 A Macics oat Weeneearets Cuthbert 4x4 Glterere 2 100 100 100 EDO ere —7° March 23 Eldorado 6x5 2 A HS, spa rere blk ot S| lah. oe HOW esa to so?) 11 LARS | Pe eer acsge ch eats | bat nears [cals costal ls. «i cha’ ete April 17 Watt 3x2 7 Tbr taertatar.| tare: Sa ethos [Se a Gitedl hase ides 2,'sb tend» Early Harvest 3x2 7 Meroe live tate tort le ete Se aalicws a