STATES RELATION'S SERVICE. 587 



hope that under normal conditions the surplus could be exported and 

 under stress they would serve to feed the population. When the 

 station was established pineapple production was in its infancy. 

 One of the earliest investigations undertaken was that of the disease 

 known as pineapple yellows. It was found that the trouble was due 

 to an excess of manganese in the soil, and that spraying the affected 

 plants with a solution of iron sulphate would control it. This can 

 be done at small expense and has made possible the replanting of 

 more than 10,000 acres on which pineapple growing had been aban- 

 doned. The growth of the pineapple industry is shown by the fact 

 that exports in 1903 were valued at $7,500 and in 1921 at $29,841,- 

 000. 



The horticulturist continued his investigations on tropical fruits 

 and especially of their propagation. During the year a modified 

 tongue graft was found adapted to the propagation of the mango, 

 96 per cent of the grafts proving successful as compared with 50 

 per cent for the best method previously emploj^ed. Attention has 

 been turned to banana growing as a possible industry, and a collec- 

 tion of 35 varieties has been brought together for further study. 

 Among them are a number of native varieties that have never come 

 into commercial planting, and some of them appear to be very prom- 

 ising. The station has introduced a number of late fruiting avoca- 

 dos to secure a continuous supply of that fruit throughout the 

 year, the ordinary varieties maturing fruit only during the sum- 

 mer season. The avocado has a high content of fat and attempts are 

 being made to utilize surplus fruits in various ways. The Zante 

 currant, or the currant grape of Greece, has been successfully intro- 

 duced, and an attempt is being made to establish its culture on the 

 semiarid hillsides and mountain sides which are of frequent occur- 

 rence throughout the island. 



For several years considerable attention has been given to the 

 growing of acid limes, not only to supply local demands but as a 

 possible source of citrate of lime and citric acid for export, and the 

 variety Kusaie has been extensively propagated and distributed as 

 the best for Hawaiian conditions. 



The agronomist has given especial attention to the development 

 of coarse forage grasses to be cut green and fed to dairy stock. A 

 rapidly growing plant that can be cut frequently is required for this 

 purpose. It has been found that Uba cane apparently meets the re- 

 quirements. In cooperation with the Hawaiian Sugar Planters' 

 Experiment Station successful attempts were made to hybridize 

 Uba cane with pollen from some of the best varieties of sugar cane. 

 Uba cane seldom flowers in Hawaii, but the station overcame this 

 difficulty and a number of hybrids are being tested for forage and 

 for sugar production. Considerable attention is being given to crops 

 adapted to rotate with sugar cane and pineapples. Pigeon peas 

 have given very promising results in rotations with pineapples. 

 Sunn hemp {Grotalaria juncea) has been found excellent as a green 

 manure crop on exhausted pineapple lands, and demonstrations with 

 it are in progress on the various islands. Hybridizing and selection 

 work with Guam and other varieties of corn and the seedling pro- 

 duction of sweet potatoes have given excellent results, and some well- 

 fixed strains have been secured for wide trial by the growers of these?. 

 crops. 



