becoming old, and therefore in less good condition and less able to function well

When the cell can't divide any more, it becomes senescent, or terminally old. 当细胞不能再分裂后，就会衰老。

Disease is favoured by wet and damp conditions and is found most commonly on mature or senescent leaves. 疾病容易在潮湿的条件下滋生，最常发生在成熟或衰老的叶子上。