It would be useful for annotation to add something to the definition of this term as follows:
Leaves that have mosaics of juvenile and adult tissues. In maize, the juvenile will be at the tip, which differentiates first, with adult at the base. Other grasses may have other arrangements, eg Brachypodium, which has both juvenile and adult across the breadth of a leaf. I got this from Erin Irish, an expert in this area. Irish, E. E. and Karlen, S. (1998) Restoration of juvenility in maize shoots by meristem culture. International Journal of Plant Science 159, 695-701.