I soaked lettuce seeds in distilled water for 12 hours.Then, I transferred them to petri dishes that had double folded filter paper moistened with distilled water. The petri dishes were then left in a room for 72 hours (Petri dishes were covered with transparent glass). After 72 hours,when I checked the petri dishes, only a small radicle had come out from the seeds and no hypocotyl could be seen. I left the petri dishes for 2 more days, but there was no further growth. Is there is problem with my seeds?
For lettuce seeds germination you must provide a temperature of at least 3-4 Celsius degrees, but the optimal is 18-20. Soaking the seeds is not necessary. The small radicle will become the tap root. A possible cause for your seeds not having hypocotil is that the radicle needed to be in a vertical position for the rest of the plant to develop. Also, it would be interesting to know how many seeds have germinated.