Solid stems are much easier to clone. Hollow ones have problems with capillary action (I am assuming) and turn to mush.
I just threw out a bunch of GG4 in RDWC that had hollow stems, 3 weeks into flower, because I neglected them, doing too many things at once. Noticed that the hollow stem plants did not respond well to supercropping. Most that were bent, never grew upwards. The branches that were not bent grew crazy tall, like GG4 is known to do in first 3 weeks of flower.
I should have moved that batch to RDWC sooner, and let veg a couple of weeks, to develop massive root system. Some were on the weak side, for RDWC.