I was out harvesting lettuce for tonights salad. We planted a lettuce mix and a mesclun mix so some things don't exactly look familiar to us as "lettuce." I have been harvesting by cutting off one or two leaves per plant off of many plants. So far two have petered out and flowered which I knew would happen. One I dug up for the compost pile and the second we liked so much we are hoping we will get to keep seed from it.
Anyway, with todays cutting I cut one that was milky down the vein when I cut it. Is this supposed to happen with some lettuces? Does it mean it is on its way out? As a child, in the city, milky always meant poisonous so I was afraid it might be a bad weed or something. I checked its base and it was something we planted because it had the little seedling sack we had origianlly started it in. I hadn't noticed it being mily before.
I have found the very easiest thing for identification purposes is to transplant. After the first round of the "Is this what we planted?" trivia game we decided to start seeds in a protected environment where weeds couldn't start and outcompete and trick us. I figure eventually we will know enough about what things look like that direct seeding will be easier but for now transplanting seems to be the way to know for sure.