While reading the comments here (http://www.reddit.com/r/todayilearned/comments/2v85tz/til_the_pink_cherry_blossoms_in_washington_dc/) I came across this quote:
The US government reciprocated with a gift of flowering dogwood trees to the people of Japan in 1915. In 1981, the cycle of giving came full circle. Japanese horticulturists were given cuttings from the trees to replace some cherry trees in Japan which had been destroyed in a flood.
But I could not find a picture of those dogwood trees. I would love to know what happened to them.
The Hibiya Park dogwoods appear to be later arrivals, based on signs at the park. Though the Japan Times reported that those trees arrived in 1915, it appears that the original dogwoods were either burned during World War II air raids or cut down as "enemy trees." The ones in the park today are descendants of the original trees.
A small park near the National Diet appears to have a cluster of dogwoods from 1960, and the Koishikawa Botanical Garden of Tokyo University may have had one until a few years ago when it died. There may be a surviving example at Tokyo Metropolitan Agricultural Horticultural High School and one at the National Institute of Fruit Tree Science in Shizuoka Prefecture. I've also seen another source say the one at Koishikawa Botanical Garden still survives.
In November 2012, 100 flowering dogwood were planted in Yoyogi Park in Tokyo. These were the first of 3,000 sent by the United States as part of the "friendship blossoms" program. The U.S. Department of Agriculture developed appropriate cultivars to survive the Japanese climate, and 1,000 will be planted in Tokyo. Another 1,000 will be planted in the Tohoku region, epicenter of the earthquake and tsunami. Another 1,000 will be distributed to schools and other organizations.
As a follow up to this (as trivia), I'll add that the U.S. sent a number of Dogwoods in 2012 to Japan. These are considered to be a gift in return for the Cherry Blossom Tress.
http://www.bridgingfoundation.org/friendship-blossom-project/overview