Environmental & other issues
Seed germination was initiated, as seen by the small radical or seed root that erupted from the seed, but has now stopped. Apparently, moisture was sufficient to initiate germination, but was inadequate to sustain it. Dry soil has caused the germination/emergence process to stop. This is common with shalllow plantings, followed by several days of hot, drying, winds. Seed in this condition can remain viable for a limited time, but if the seed becomes soft and spongy, the chances of it regrowing are not good.