Xu Kai (徐鍇), the author of 《說文解字繫傳》 (10th century AD) gave the following explanation: Pictogram (象形): 禾(“plant”) + 乃, resembling a fruit/an ear hanging off a plant.
According to Chi (2010), the character is an ideogrammic compound (會意): 禾(“rice plant”) + 引(“to draw out flowers”) — blooming of a rice plant. The Shuihudi Qin bamboo texts (睡簡) recorded this character as ⿱禾引. The bottom component 弓 found in the stone drum inscriptions is likely a reduction of 引.
May be a causative of 褎 (OC *lɯws, “growth of seedlings”). Compare Proto-Vietic*m-loh(“to blossom”) (whence Vietnamesetrổ(“to burst, to open, to display”), lổ(“naked”)), and Khmerលាស់(lŏəh, “to grow, to blossom, to prosper”).