The theories of the plant apical (shoot) meristem development are the hardest to learn in Botany.
I just hated plant morphoanatomy.
Talk about phytopenetration.
“During pollen germination, the tube cell elongates into a pollen tube. In the flower, the pollen tube then grows towards the ovule where it discharges the sperm produced in the pollen grain for fertilization. The germinated pollen grain with its two sperm cells is the mature male microgametophyte of these plants.”