Have you got a little fan on them? They need to strengthen their cute little stems. Sounds strange how they could stretch under the 400......I usually leave em under a shop light until they get a few leaves. You can really put the light right on top of them to keep them from stretching. I had some once that stretched and the stems were weak, so I propped em up with chopsticks. Hope I'm not being bossy or anything, just trying to help....

The moral of this story is: Always ask for chopsticks at chinese restaurant...