形成层

vascular cambium (layer of tissue responsible for growth inside wood)

to appear / to look / form / shape

to form / to take shape

surname Cheng

to succeed / to finish / to complete / to accomplish / to become / to turn into / to be all right / OK! / one tenth

layered / stratified

to pile on top of one another / layer; stratum / floor (of a building); story / (math.) sheaf / classifier for layers