28 BULLETIN 71, HAWAII EXPERIMENT STATION 



genial variety. However, the possibility is usually rare, because 

 many of the embryo sacs fail to develop. 



In commercial orchards in California, the rarity of congenial 

 varieties capable of fertilizing the flowers of navel oranges is 

 evinced by the small percentage of seeds in the fruits, even when 

 grown at no great distance from lemons and Valencia oranges. 

 Assuming the congenial variety to belong to the same species, 

 the Valencia orange may be concluded to furnish the pollen 

 naturally fertilizing the flowers of navel varieties. The pollen 

 of the Valencia, a variety of few seeds, is likely low in fertilizing 

 power, which fact may influence the setting of few seeds in the 

 navel variety. Results have been different at the Hawaii station. 

 During the past 10 years several crops of navel oranges with 

 abundance of seeds have developed. The orchard is a mixed 

 planting of a number of species and varieties of citrus. Condi- 

 tion for pollination were unusually favorable at certain times. 

 Although any of a number of citrus might have produced the 

 pollen, the Hawaiian orange (fig. 3) is thought to be the congeni- 

 al variety causing the navel orange and the Victoria pomelo to 

 produce large numbers of seeds. The Hawaiian orange is known 

 to have been propagated almost entirely by seeds for 140 years 

 and to have strong seed-producing habits. 



After carefully studying citrus species in southern Asia, 

 Bonavia (6, p. 37-38) concluded that the pomelo is most closely 

 allied to the Malta sweet orange. His conclusion was based on 

 the following conspicuous characters, common to both : the pom- 

 elo and the sweet orange are the only two citrus species having 

 varieties with reddish pulp ; great similarity is seen in the leaves, 

 both having winged petioles, in the emarginations of the base of 

 the pulp carpels of the fruit, and in an occasional navel form 

 of fruit (fig. 1, A, pomelo on the right with navel in stigmatic 

 part) . 



At the station investigation is under way to ascertain the 

 possibilities of producing regular seedless crops of both the Vic- 

 toria and the Siamese varieties of pomelo. Isolated plantings 

 have been made and experimental pollinations planned to deter- 

 mine definitely what species or varieties are congenial and 

 whether the pomelos are absolutely self -sterile. 



VARIETIES OF GRAPEFRUIT 



Grapefruit propagating material was first obtained by the 

 Hawaii station from Florida in 1906. From this material, trees 

 of budded varieties were developed and set in orchard form in 

 1909, 1910, and 1911. The stocks used were sweet orange, 

 grapefruit, sour orange, and rough lemon. Conditions in the 

 orchard have not always been entirely favorable during the 22 

 years of its existence. Probably the most serious drawback to 

 good culture has been insufficient moisture for considerable peri- 

 ods during several dry seasons. An improved water supply in 

 recent years has largely overcome this difficulty, but the nature 

 of the soil and the arrangement of the trees do not permit the 

 proper application of water for best cultural results, particularly 

 for control of the so-called gum diseases. The experiments have 



