14] 



VEGETATIONAL TYPES OF TROPICAL LANDS 



437 



to a greater depth than usual— e.^. in sHght hollows or the angles 

 between the buttresses of trees — but they may be absent from 

 considerable tracts, especially in rain forest with a marked dry 

 season. For in general there is very little humus accumulation in 

 the tropics, owing to the rapidity of decay and breakdown of 

 organic matter. The forest floor normally is barely covered by a 

 thin litter of leaves, and commonly shows through in frequent 

 bald patches. 



Fig. 150. — Flower and buds «f Rifflesio inanillana, a true parasite on the roots 



of a Cissiis vine. Rafflesia has no regular leaves or stem, and no chlorophyll, the 



flowers growing directly from the roots of the host; an allied species, R. aruoldii, 



has the largest known flowers (about a metre in diameter). 



7. Parasites. Of these there are, apart from Fungi and Bacteria, 

 two main synusiae in the tropical rain forest — the root-parasites 

 growing on the ground (Fig. 150) and the semi-parasites (often 

 termed hemiparasites) growing epiphytically on the trees. The 

 former are few^ and of little importance, comprising two small but 

 remarkable families. On the other hand, the epiphytic semi- 

 parasites all belong to the Mistletoe family (Loranthaceae — Fig. 

 151) and are numerous in species and often abundant, being met 

 practically throughout the area of the rain forest. They are woody 

 shrubs that in forests of fair density occur on the twigs and branches 



