The inter stock trees were smaller than the non-inter stocked trees and yielded slightly less fruit. Of considerable interest is the fact that when the Cleopatra was inter stocked to itself, inserting a 15-cm interstem at 15 cm, the trees had less yield and smaller canopies than any of the inter stock trees or the noninter stocked trees. A similar comparison using Cleopatra as the inter stock on Troyer citrange root stock is shown in Table 9. The critical height of interstem insertion appears to be slightly higher on Troyer citrange than on Cleopatra mandarin, as in the height of budding experiment. Maximum yield occurred at the 30-cm interstem insertion rather than at 15 cm. Largest tree size occurred at the 5-cm insertion, but the second largest trees occurred at the 30-cm level—with less yield and smaller tree size when the interstem was inserted above that level. While there was little difference in yield and tree size of the Valencias on Cleopatra budded at the 15-cm level to the 15-cm interstem insertion, in the case of the scion budded directly on Troyer at the 15-cm level, both yields and tree size were significantly greater. The inter stocked trees had lower yields and smaller canopies than the non-inter stocked trees. When the Troyer root stock was inter stocked at 15 cm with a 15-cm interstem, the trees were about half the size of those without the interstem,vertical farming in shipping containers and yielded considerably less fruit. It is significant that both root stocks budded to themselves have the same type of results. In both reciprocal grafts using a constant length inter stock but increasing the height of insertion, there was no effect on fruit size or fruit quality other than root stock effect.Leaf analysis of these combinations showed some slight differences in nutrient levels.

However, with all combinations, both the macro- and micro-elements were within the normal range, and the principal effect was from the root stock. In the second part of the experiment, the interstem was inserted at a constant level of 15 cm, but the length of the inter stock was 5, 15, 30, 45, and 60 cm budded to Valencia orange. Thus only the length of the interstem was changed. Trees without an interstem budded at 15 cm served as checks. There is also a comparison with the self-inter stocked trees. The effect of length of Troyer citrange inter stock insertion on yield and canopy volume of Valencia orange on Cleopatra mandarin root stock is shown in Table 10. Results obtained with variable inter stock lengths, inserted at a constant level, vary greatly from different heights of inter stock insertion. Canopy volume is greatest with a 15-cm interstem and tends to be reduced with increased length of interstem. Canopy volume of the inter stocked trees is slightly less than the non-inter stocked check trees. Yields show no correlation with tree size. Lowest yields were obtained with a 30-cm intermediate, but yields were higher with both shorter and longer inter stocks. Both average yields and tree size were somewhat comparable to those of non-inter stocked check trees budded at 15 cm. However, when the root stock was inter stocked to itself, both yield and tree size were greatly reduced. Data for the effect of length of Cleopatra mandarin inter stock insertion on Troyer citrange root stock is shown in Table 11. It is quite apparent that, when the height of the interstem insertion is constant, the length of the interstem has little or no effect on tree size. The average yield per tree was very erratic and showed no trends. Highest yields were at the 15- and 45-cm lengths, next highest at the 30- and 60-cm lengths, and lowest at the 5-cm length. Average yield of the inter stocked trees was slightly less than half that of the standard non-inter stocked trees, and tree size was about two-thirds as large. The combination inter stocked to itself yielded less fruit than the reciprocally inter stocked trees, but tree size was slightly larger. There was no significant effect of the length of inter stock on fruit size, fruit quality, or nutrition.

It would appear that the height of the inter stock insertion has a much greater effect than the length of the inter stock. The question is always raised in inter stocking as to what effects are attributed to the double bud union and what effects arise from the interstem piece. It is possible that this might be answered by inter stocking each root stock to itself. The fact that these effects occurred with both root stocks used is significant. A reasonable explanation of why the effects of selfinter stocked root stocks were greater than the reciprocally inter stocked ones is not presently available and needs to be investigated further. Nauriyal, Shannon, and Frolich had some difficulties with a 2.5- cm inter stock insertion in the Eureka lemon-Troyer citrange incompatibility, but after an initial disharmony, the trees recovered and remained normal in appearance. Russo reported a difference of sweet orange inter stock in the growth of Monachello lemon on sour orange stock in Italy. An Ovale orange inter stock produced a good union with both the sour orange and lemon junctures, and most of the trees showed no decline after 25 years of age. However, a Moro blood orange sandwich behaved differently, producing a good union with the sour orange, but did not avoid the overgrowth of the lemon scion. When an Avana mandarin sandwich was used, it grew more slowly than either stock or scion and showed a constriction of the inter stock, but after 25 years, the trees were normal in appearance. Labanauskas and Bitters found that five trifoliate orange cultivars, when used as inter stocks on sweet orange root and budded to Valencia orange scions, had no significant effect on mineral nutrient content of the scion variety when compared to trees on sweet orange root stock with no inter stock. Iwasaki, et al. inter stocked the vigorous strain Tachikawa satsuma with Noda, a dwarf satsuma strain, as well as with Yuzu and C. tachibana, all on trifoliate orange root stock, and summarized effects after ten years of observation. The inter stocks of the dwarf satsuma strain showed less vigor, less yield and less growth of the root stock with progressive effects as the trees became older.

Trees on the C. tachibana inter stock were the most vigorous and correspondingly gave the best yields; those inter stocked with Yuzu, the poorest. Effects were somewhat complicated by apparent incompatibility and stem pitting. Mielke and Issa reported on the effects of several inter stocks on fruit quality of Red Blush grapefruit on Cleopatra mandarin root stocks. Interstocks used were two local selections of sour orange, two unidentified mandarin types, chinotto orange, C. depressa, C. sunki, and C. amblycarpa. In general, slightly smaller fruits resulted with the C. depressa and C. sunki inter stocks and those on chinotto inter stock were slightly larger. One of the unidentified mandarins increased peel thickness and one of the local sours and C. amblycarpa reduced peel thickness. No effect was noted on juice content,vertical grow racks total soluble solids or total acidity. However, soluble solids to acid ratio was generally lower with C. sunki inter stocks and higher with the chinotto inter stock. Khalidy , using root stocks of sour orange, Rough lemon, trifoliate orange, grapefruit and sweet orange, reciprocally inter stocked them, as well as with a Valencia intermediate, and budded them to Valencia scions. He states that, when trifoliate orange was used as an inter stock in field plantings, it appeared capable of decreasing plant growth. However, when more vigorous citrus species were used as intermediates, they did not enhance plant growth. There was no effect in the greenhouse with inter stocks after 11 months. Perhaps his experiments did not progress long enough, and maybe two replications were inadequate. He also found that, in certain cases, the inter stock species appeared to influence the ratio of total solids to total acids. A root stock which induced a higher ratio also induced a higher ratio when used as an inter stock. Khalidy also found that, when Rough lemon was used as an inter stock, it appeared to decrease the transpiration rate of the combination, but to a lesser extent than when it was employed as a root stock. On the other hand, when sour orange was used as an inter stock, it did not impart an increased transpiration rate as it did when used as a root stock. The inter stock species in certain cases did exert definite effects upon the inorganic composition of scion leaves. However, it was not necessarily in the same direction as the influence it imparted as a root stock.

Root stock effect on inorganic composition in most cases predominated over the inter stock effect. In his studies, Khalidy also found that boron content of the scion leaves was less with a sour orange intermediate, but that a Rough lemon inter stock appeared capable of increasing boron content. His studies indicate that there are cases where the inter stock behaved similarly, as when it was employed as a root stock, and still other cases where the inter stock effect was opposite to that when it was used as a root stock. Gardner double budded Hamlin and Valencia sweet orange trees with inter stocks of Rough lemon on sour orange root stock and sour orange inter stocks on Rough lemon root stocks. The sweet orange varieties were also budded directly on these two root stocks. The inter stocks were of two lengths, 7.5 cm and 15 cm. After six years in the field, there were the usual differences between Rough lemon and sour orange in tree size, yields and fruit quality of the scion variety, but there were no significant differences caused by the inter stocks. Gardner concluded that the results indicated that the root stock was the only controlling factor influencing tree growth, yield and fruit quality and that the inter stock did not alter the root stock influence in any of these aspects. In Israel, Safran and Bental used inter stocks of sour orange, Rough lemon and sweet lime with Shamouti orange, with Shamouti on sour orange as checks. The results were very much confused by the presence of stem-pitting . The Shamouti/sour orange/Rough lemon combination made strong trees with the highest yield of all the double-worked combinations, but not as good or productive as the Shamouti on sour. A high percentage of the trees with sweet lime as an inter stock declined or remained small and was accompanied by severe stem-pitting. There was slight stem pitting on the Rough lemon and a bud union malformation at the juncture of the Shamouti on Rough lemon. Robinson reported that various tangelos, as well as the Temple orange , when grown directly on Rough lemon root stocks in Florida tend to produce fruits which become puffy, coarse, semi-dry, and pithy as they reach maturity. If the Rough lemon root stock was originally budded to grapefruit or sweet orange scions and then top worked to the mandarin hybrids, the following crops did not produce the adverse fruit effect referred to above. Strong inter stock effects like these are not typical. Webber reports that in a letter he received in 1943 from W. M. Mertz, a small orchard near Upland, California, was planted about 1903 to tangerines on sour orange root stock. The trees were top worked to lemons about 1931. As of 1943, Webber reported the orchard was making good growth and satisfactory yields. The author visited this same orchard several times in the mid-fifties and perhaps as late as the mid-sixties. The planting was still productive and in excellent condition, but probably soon afterwards succumbed to a housing development. Lemon trees top worked onto orange trees, regardless of root stock, have done very well. Again, Webber discusses a letter from W. M. Mertz received in 1943. Mertz described two orchards in Orange County, California, in which navel oranges on sour orange root stock were top worked to lemons. In 1941, the original root stock and sweet orange “sandwich” were 45 to 50 years old and the lemon tops were 26 years old.