Sclerenchyma and Idioblasts
Mesophyll is often interspersed with sclerenchyma, particularly at leaf margins and extending as girders from the vascular bundles to the epidermis. Fibres are typically found in groups associated with the vascular bundles or leaf margins, but sclereids are normally isolated in the mesophyll. For example, star-shaped astrosclereids occur in leaves of Nymphaea and petioles of Camellia (Fig. 1.8). Osteosclereids are characteristic of species with centric leaves, such as Hakea. In some species sclereids are associated with veinlet endings.
Other types of idioblast may also be interspersed in the mesophyll. For example, secretory myrosin cells are often found in the leaves of many Brassicaceae, and laticifers occur in leaves of angiosperms, especially those of some eudicots such as Euphorbia and Ficus.