I bought a dendrobium about a week and a half ago. When it arrived, the roots looked very dry and some seemed hollow. I trimmed the hollow feeling roots and potted it, but I noticed the bottom leaf of one of the canes yellowing today and unpotted it to have a look. I've never grown orchids before, are these roots dead? I've rinsed them off to show them as clearly as possible. I was watering about every three days, I was worried about those dry roots. Should I trim any more of these roots? How about fungicide? Any way to stimulate new root growth?