Looks like heat stress, and a few other factors... make sure you have adequate ventilation and that the temperature doesnt exceed 78F. I say heat stress because several of your plants are showing tall defined ridges on the leaves.

Also it looks like you are using fluorescent lights for your grow, i dont think your plants are getting enough light, but maybe its just the pictures. And i have to ask... are these bagseed plants? If they are, dont expect too much from them, there is a reason they call it schwag!

One more thing, what kind of soil are you growing these plants in? It doesnt look great for growing weed to me, lots of bits and pieces in the soil, can drastically change the drainage characteristics of the soil. Consider getting some soil from Casa de Pot (Home Depot) like Scott's. And last but not least... what nutrients are you using??? At least add some bone and blood meal if you cant afford the real stuff, and if you can i recommend Advanced Nutrients.

Good luck with the grow, Peace.