14] VEGETATIONAL TYPES OF TROPICAL LANDS 425 



affecting the whole vegetation, flowering and fruiting going on all 

 the time, though with particular species tending to have their own 

 definite seasons in these and some other respects. Thus whereas 

 in some species the different individuals may lose their leaves at 

 entirely different times, more often there is approximate synchroniza- 

 tion of this event between them each year — but not between members 

 of different species to nearly such an extent as in most temperate 

 forests. The dormant buds are most often small and unprotected, 

 but frequently develop after several or many years, so giving rise to 

 ' cauliflory ' (the formation of flowers on old ' bare ' wood), which 

 is particularly common in these regions. 



The main plant components of the tropical rain forest are normally 

 the following seven : 



I . The forest trees. These form the main structural component, 

 sometimes referred to loosely as the ' roof ' or ' canopy ', which is 

 typically made up of three more or less separate strata characterized 

 by different types of trees. These ' stories ' or ' layers ', as they 

 are also called, are usually ill-defined and indeed seldom easy to 

 recognize by casual observation, owing to the fact that species of 

 all manner of intermediate heights are commonly present, while 

 upgrowing young trees may be of almost any height up to the stratum 

 to which their kind belong, and even different component species 

 of a stratum often have different heights. In general, however, 

 there can be distinguished strata consisting of trees whose crowns 

 vary in height about a mean, and commonly there are three such 

 strata in tropical rain forests. 



The roof of the forest has usually an irregular profile, the trees 

 of the highest (A) stratum being often more or less widely spaced 

 and rarely forming a continuous layer to which the term ' canopy ' 

 may be applied. The second (B) stratum, or sometimes even the 

 third (C), is commonly the highest layer of tree crowns forming a 

 continuous mass. The crowns of the B stratum typically extend 

 from about 15 to 30 metres in height, while the still shorter trees 

 composing the C storey are usually small and slender and have 

 narrow tapering crowns commonly 5-15 metres high. Fig. 141 is 

 a profile diagram of typical mixed rain forest in British Guiana in 

 which the three tree strata are barely recognizable. When, as in 

 this case, the two upper strata are much broken, the third is usually 

 dense ; but when the upper ones are dense the third is apt to be 

 much less well developed— as in Fig. 142. In the former circum- 

 stances Palms may be prominent, as in the example shown in 



