At the break Root was 178 not out, having resumed on 114, and England was 379-5 in reply to New Zealand's 375. Root had put on 117 in an unbroken partnership with Ollie Pope, who was 46 at lunch after being 4 not out overnight.
Runs came slowly for England for much of the morning. Root and Pope added 42 runs by drinks in the first half of a session extended to 2-1/2 hours because of rain the previous day. A further 68 runs came between drinks and lunch as Root noticeably stepped England's scoring rate but continued to be cautious.
New Zealand was on the defensive for most of the morning on a wicket which was playing slower and lower. By bowling full and straight and employing a split, five-four field it was able to stop Root scoring on the drive down the ground.
The slowness of the pitch and a lack of bounce made it difficult to score behind square, but Root and Pope adapted themselves well to the challenge, sweeping spinner Mitchell Santner and dabbing the quicker bowlers down to third man.
Root reached 150 in 8-1/4 hours and from 335 balls in a major feat of concentration for a player who entered the series out of form. He had scored only 321 runs at an average of 26 with three half centuries since the start of the English summer.
His century was the 22nd of his career but his first since February, and was also his slowest, taking almost six hours. Pope provided stalwart support, steadying England after it lost the wickets of Rory Burns, Ben Stokes and Zak Crawley in the late stages of the third day.
By lunch the young No. 6 had batted almost three hours, hitting only four boundaries. England's purpose, other than to eke out a first-innings lead, hasn't been entirely evident so far on the fourth day. Trailing 1-0 in the two-match series, England must win this test to avoid a series defeat.
To do so it will have to establish a substantial lead, then give itself time to bowl out New Zealand on a pitch which is offering little to the faster bowlers. The evidence of Root's innings is that survival is possible despite the slowness and low bounce.
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