Impressed by the low bid for the construction contract submitted by the engineering firm Fox, Henderson and Co, the commission accepted the scheme and finally gave its public endorsement to Paxton's design in July 1850. He was exultant, but now had less than eight months to finalize his plans, manufacture the parts and erect the building in time for the Exhibition's opening, which was scheduled for 1 May 1851. Paxton was able to design and build the largest glass structure yet created, from scratch, in less than a year, and complete it on schedule and on budget. He was even able to alter the design shortly before building began, adding a high, barrel-vaulted transept across the centre of the building, at 90 degrees to the main gallery, under which he was able to safely enclose several large elm trees that would otherwise have had to be felled—thereby also resolving a controversial issue that had been a major sticking point for the vocal anti-Exhibition lobby.