In monocot leaf

The correct option is "Mesophyll is not differentiated into palisade and spongy parenchyma".

Let us understand the anatomical features of a monocotyledonous (monocot) leaf step-by-step to see why this option is correct:
1. Mesophyll structure: In monocot leaves, which are typically isobilateral (having similar upper and lower surfaces), the mesophyll tissue is uniform. Unlike dicot leaves, the mesophyll in monocot leaves is not differentiated into palisade parenchyma (long, vertically arranged cells) and spongy parenchyma (loosely packed, spherical cells with air spaces). Instead, it consists of more or less similar-looking green parenchymatous cells with intercellular spaces.
2. Venation pattern: Monocot leaves display parallel venation where the veins run parallel to each other, rather than forming a reticulate network. Therefore, the option "Veins form a network" is incorrect.
3. Presence of Bulliform cells: In many monocot leaves (especially grasses), large, empty, colorless cells called bulliform cells are present in the upper epidermis to help the leaf roll and unroll to regulate water loss. Thus, the statement "Bulliform cells are absent from epidermis" is incorrect.
4. Therefore, the characteristic feature of a monocot leaf is that its mesophyll remains undifferentiated.