Any hydroponic plant has hollow stems, due to the excess of water, the plant doesn't fill that space up with the capillarious(totally made that word up but heres the definition, and it makes sense, I think Websters should hit me up) the "meat" as you would call it, or the fibrous material inside the stem which transfers the water from roots to the rest of the plant without using osmosis, it simply wicks the moisture up, in a hydro plant, or I guess the strain your dealing with, the plant just has everything it needs and can do it easier than others, making it produce less meat. This could be wrong, but its what comes to mind when I thought about this, read it somewhere in school a bit ago.

-C