I I'Z 



THE SUBDIVISIOXS OF THE VEGETABLE KINGDOM. 



in the form of switch-shrubs, and several Asclepiadacese, e.g. the species of the genus 

 Stapelia, have cactiform stems. In these the assimilation of carbon is efiected by 

 the green cortical tissue. The Orobanchacese are parasites destitute of chlorophjdl 

 (see vol. i. p. 183). Amongst Convolvulacese, and more especially amongst Scrophu- 

 lariacere, there are many species which live as parasites and saprophytes, and are 

 partiallj- deficient in chlorophyll (see vol. i. pp. 171-1S3). An account has already 



,--,:',iia?.i_ 





Fig. 431. — Aciuilhaceffi. 

 Acanthus niollU on the coast of Dalmatia. 



been given of the way in which the Lentibulariacepe, e.g. the species belonging to 

 the genera Utricularia and Pinguicula, derive a portion of their food from the 

 bodies of insects which are caught by them (see vol. i. pp. 120, 140). In Gentianaceae, 

 Oleacese, Apocynaceae, Asclepiadaceae, Convolvulacese, and many Boraginaceae and 

 Solanaceae the corolla is actinomorphic. The Labiataj, Scrophulariacece, Verbenaceae, 

 Acanthaceae, Lentibulariacete, and some genera of BoraginacefB and Solanaceas bear 

 distinctly zygomorphic flowers. In the Ash genus {Fraxinus), which belongs to the 

 family of Oleacea, the corolla is often entirely suppressed. Most Labiatae have four 



