2012 A TEXTBOOK OF THEORETICAL BOTANY 



to that developed by the aerial roots of Orchids. If they reach the soil they 

 produce underground branches. The stems are normally sympodial, each 

 segment bearing one or more scale leaves before producing a foliage leaf. 

 The axillary shoots are often adnate to the main axis. 



The leaves are very variable in form. In some they are narrow with 

 parallel venation. In others they are large, pinnately veined or net- 

 veined and divided into lamina, petiole and sheathing leaf base. In 

 Monstera and related genera, holes are produced in the course of 

 development between the lateral veins owing to the cessation of growth 

 over certain small areas. As a result of the holes the leaves may 

 eventually become pinnately dissected. In Philodendron cuneifolium the 

 petioles serve as water reservoirs and contain large intercellular spaces 

 lined with mucilage which fill with water after rain. 



Latex is present in many genera. It is formed in sacs associated with the 

 phloem both in stems and petioles. The longitudinal arrangement of the 

 latex sacs is more typical of this family than an anastomosing system of 

 canals. Large internal hairs are present in the ground tissue in several 

 genera, such as Monstera, projecting into the intercellular spaces. 



The classification of the family is variously interpreted. Engler recog- 

 nizes eight sub-families, while Hutchinson prefers to arrange the genera 

 into eighteen tribes. Since it is only possible here to discuss the genera very 

 briefly we shall follow the simpler Englerian system, though it must be 

 realized that in such a diverse group only a very detailed study of the 

 various genera could produce a truly phylogenetic system. 



I. Pothoideae 



Land plants without latex. Leaves developed in two ranks or spirally 

 arranged. Flowers usually hermaphrodite. Eleven genera, including Pothos, 

 Anthuriiim, Acorns. 



II. Monsteroideae 



Land plants without latex. Flowers hermaphrodite, usually naked. 

 Eleven genera, including Rhaphidophora, Motistera, SpathiphyUiim and 

 Epipremniim. 



III. Calloideae 



Land or marsh plants possessing latex. Leaves never sagittate, flowers 

 hermaphrodite or unisexual. Three genera: Symplocarpus, Lysichiton 

 (Fig. 1949) and Calla. 



IV. Lasioideae 



Land or marsh plants possessing latex. Leaves sagittate. Flowers 

 hermaphrodite or unisexual. Seeds usually without endosperm. Nineteen 

 genera, including Draconitum, AmorphophaHus. 



V. Philodendroideae 



Land or marsh plants possessing latex. Leaves usually parallel-veined. 

 Flowers unisexual, seeds endospermic. Nineteen genera, including Philo- 

 dendron and Zantedeschia [Richardia). 





