Lack of incorporation of tritiated uridine by nuclei of mature sieve elements in Metasequoia glyptostroboides and Sequoiadendron giganteum.

The majority of nuclei which persist in "mature" sieve elements of Metasequoia glyptostroboides Hu and Chen and Sequoiadendron giganteum Buchholz fail to incorporate tritiated uridine (10 μCi/ml; 7 hours incubation of stem fragments). This is interpreted as further evidence for the degenerated condition of these nuclei.