"The leaves of spring"
Translation:Dail y Gwanwyn
In a possessive construction "the A of the B", the pattern in Welsh is A y B. The first noun (A) can't have an y before it, only the second noun (B) can.
"the top of the mountain" pen y mynydd
"the back of the bus" cefn y bws
"the leaves of the spring" dail y gwanwyn
There's a short video explaining it here: https://www.youtube.com/watch?v=OUuvCwOHs2c
And here's a more detailed description of the construction: https://www.reddit.com/r/learnwelsh/comments/5oqafl/welsh_grammar_the_genitivepossessive_construction/?st=izfl71il