44 -^ 



Till-; JoiKXAi. oi' Hl•;Kl■:l)^r^• 



Siam, but in many lowland countries 

 in that part of the worid. The explana- 

 tion is that the land has been reclaimed 

 from the sea, by the construction of 

 successive levees about 12 feet wide 

 and six feet high. The space between 

 these is a ditch 12 feet wide and six 

 feet deep, which is used as an irrigation 

 trench, from which water is thrown by 

 men equipjicd with bamboo paddles, 

 to the trees ])lantcd above their heads 

 on the levees. The trees are set about 

 12 feet apart in the row. the rows being 

 15 feet apart. The soil is of a very 

 heavy texture, 50% to 60% clay. No 

 cultivation is practiced, other than to 

 keep the levees cleared of weeds. 



The ]Jomelos here were inferior to 

 those secured later. Two trees pro- 

 duced jjyriform fruits which proved to 

 be absolutely seedless, but on the third 

 tree of the same type in the same row, 

 one fruit out of every half dozen con- 

 tained seeds. The best fruits which I 

 secured were from Chinese orchards in 

 the Nakon Chaisii district. The largest 

 orchard there contained 48 acres of 

 land, 36 acres being planted with 

 ordinary, seedy pomelos and the re- 

 maining 12 acres with trees of the 

 seedless type. The same system of 

 jjlanting was used here as in Prince 

 Yugelar's garden, and the composition 

 of the soil was about the same. All 

 l^lants arc propagated by marcottage, 

 fjudding being so entirely unknown 

 that the gardeners thovight it a prac- 

 tical joke, when shown how to insert 

 buds as the best method of pro]:)agation. 



I made a thorough investigation of 

 several trees in the seedless section of 

 the grove, cutting open fruits from 

 widely separated points on each tree. 

 All these trees bore seedless fruits, but 

 in some cases seedy fruits were also 

 produced, jjarticularly by trees that 

 stood on the side of the grove nearest 

 the ordinary, seminiferous ])omelo trees. 

 The native gardeners believe that the 

 sccdlessness of their ])omelos is due to 

 the use of salt, a coconut shell full of 

 which is ]jlaced around the roots of 

 each tree planted, while brackish water 

 which backs ujj between the levees is 

 used for irrigation. My own investiga- 

 tion convinced me that we have to do 

 here with genuine seedless types, which 



however are ca])able of ])roducing seeds 

 when cross-pollinated. On this theory, 

 the occasional seedy fruits there pro- 

 duced are the result of i)ollen from trees 

 in the adjoining orchard, carried by the 

 wind or insects to the flowers of the 

 normally seedless trees. The discon- 

 certing behavior of the t''ee in our 

 greenhouse at Washington, which bore 

 such seedy fruit, is then to be attributed 

 to cross-pollination by some other 

 variety of citrus, of which there were 

 a niimber in the same greenhouse. 



INFLUENCE OF POLLEN. 



Due to the shortness of time available 

 for this investigation, I was not able to 

 prove this theory by an investigation 

 f)f the flowers of the trees in question. 

 But from experience which I gained 

 while working as Assistant in Arbori- 

 culture in charge of the propagation of 

 citrus fruits under W. T. Swingle of the 

 U. S. Department of Agriculture at 

 Washington, I am satisfied that this 

 theory fully accounts for the phenomena 

 observed, that it is in accord with our 

 experience on other seedless citrus 

 fruits, and that there is no other theory 

 which will account for the beha\'ior of 

 these pomelos, so simj^ly and com])re- 

 hensively. 



The behavior of navel oranges, in 

 which seeds are very rarely found under 

 normal conditions, seems to me to be 

 an exactly analogous case. E. M. 

 Savage, Assistant Plant Breeder, office 

 of Crop Phy.siology and Breeding In- 

 vestigations, who made a large number 

 of crosses of Citrus trijoliata on Wash- 

 ington navel oranges in California in 

 1909. for the purpose of producing new 

 varieties of navel oranges ha\-ing a frost 

 resistance, tells me that while ])erfoiTn- 

 ing this work in the groves of L. \'. W. 

 Brown of Riverside, California, he 

 found a number of navel oranges which 

 bore seeds. These were observed to be 

 growing near ])omelo trees, and he 

 believes their seediness was due to the 

 influence of pomelo pollen. Mr. Savage 

 also stated that whenever the navel 

 was from 50 to 100 feet away from the 

 pomelo trees, all of the fruits ins]x>cted 

 were found to be seedless. 



Similar results were reported in 



