In $Opuntia$ (prickly pear),the spines are modified forms of:

Describe the various parts of a leaf.

Which one of the following is not an example of developmental heterophylly?

Reticulate venation is found in dicot leaves,while in monocot leaves,venation is of the parallel type. Biology being a 'Science of exceptions',find out any exception to this generalization.

Unifoliate compound leaf is found in

In the given diagram of a leaf,what are $P$ and $Q$?
$P \quad Q$