10 BULLETIN 3 3, PORTO RICO EXPERIMENT STATION 



ferric chloride solution should next be added. The mixture should 

 then be poured into a measuring cylinder and thoroughly stirred, 

 and water added to make 50 cubic centimeters. The color produced 

 by the ferric chloride when mixed with the root bark of sour orange 

 is very black. With cultivated grapefruit it is much lighter, and 

 with native grapefruit it is still lighter, whereas with lemon prac- 

 tically no color develops. 



The roots should preferably be taken from trees that are growing 

 vigorously, as dormancy may interfere with results. When the color 

 is not distinct enough, the following laboratory method may be satis- 

 factorily used : Add a small portion of aluminum cream to the mix- 

 ture and filter by means of vacuum. The depth of the color of the 

 different solutions can then be determined in a colorimeter in com- 

 parison with a standard solution of naringin to which ferric chloride 

 has been added. Lemon shows practically no color change; native 

 grapefruit has a color equaling 4 to 6 milligrams naringin in 50 cubic 

 centimeters of water; cultivated grapefruit has a color equaling 6 

 to 10 milligrams naringin, and sour orange has a color usually much 

 deeper than 10 milligrams. 



The rough or goat lemon, locally known as limon de cabra, has been 

 and still is used extensively for stock. Unfortunately the method of 

 identification does not permit of differentiating between the different 

 varieties of lemons, but growth characteristics indicate the probable 

 use in some instances of a variety other than rough lemon. The vis- 

 ible characters of trees which have been budded on lemon stock are 

 (1) comparatively vigorous growth regardless of soil type, and (2) 

 an uneven bud union, with the trunk usually enlarged below the 

 union. (Fig. 4, A.) Frequently the enlargement is visible on trees 

 5 to 10 years old ; after that time it may be obliterated. Trees having 

 received little cultivation and small amounts of fertilizer up to 10 

 years of age may not show enlargement. (Fig. 4, B.) On the other 

 hand, grapefruit trees on lemon stock may be decidedly constricted 

 below the bud union, a condition which would indicate the probable 

 use of some variety less vigorous than the rough lemon. 



The sour orange {Citrus aurantium), commonly called naranja in 

 Porto Kico, was used considerably as budding stock 25 years ago, and 

 trees budded on it can be found in most of the older groves. Trees 

 on sour-orange stock usually are (1) smaller than those on lemon or 

 grapefruit stock, and (2) where grapefruit was used, constricted be- 

 low the bud union. (Fig. 5, A.) In one grove having a loose, fri- 

 able loam soil, trees 25 to 28 years old on lemon and sour-orange 

 stocks were found to be of practically the same size. In another 

 grove having an extremely light sandy soil, 25-year-old trees on sour- 

 orange stock were dwarf in comparison with those on lemon stock. 

 The same was observed in several groves having an extremely heavy, 

 poorly aerated soil. Constriction below the bud union develops 

 especially when the trees are well cultivated and fertilized. With 

 no cultivation and scant fertilization, the growth is slow, and the top 

 may develop no faster than the stock. When sweet orange is budded 

 on sour-orange stock, the bud union usually is smooth, and constric- 

 tion does not develop. 



