A.T. Robertson Commentary Mark 4:8

"And others fell into the good ground, and yielded fruit, growing up and increasing; and brought forth, thirtyfold, and sixtyfold, and a hundredfold." — Mark 4:8 (ASV)

Growing up and increasing (αναβαινοντα κα αυξανομενα). In Mark alone. A vivid detail enlarging on the continued growth implied in the imperfect "yielded fruit" (εδιδου καρπον). It kept on yielding as it grew. Fruit is what matters.