268 Eduard Riibel 



stem-flowering (caulifloral) trees, usually without bud protec- 

 tion and with glabrous and glossy foliage. The climate this forest 

 needs is hot oceanic, as found in the tropics. The tropical coun- 

 tries have an annual precipitation of from two hundred to four 

 hundred centimeters, distributed rather evenly the year round. 

 The mean annual temperature is high and uniform, the differ- 

 ence between the warmest and the coldest months being only 

 from one to six degrees Centigrade. The vegetation looks lux- 

 uriant. As many as four or five stories are developed. It is 

 the phanerophyte climate of Raunkiaer, in which high-grown 

 species are plentiful. Warming (1892) counted four hundred 

 species of trees within three miles' distance in Lagoa Santa, 

 Brazil. Light is a minimum factor within the forest. The leaves 

 are evergreen, though the single leaf lives not much longer than 

 one year ; but the defoliation is irregular the year round, so that 

 the forest never stands bare. Rain forest is distributed in the 

 tropics of Australia, Ceylon, the Sunda Islands, Annam, New 

 Guinea, Central America, northern Brazil, and Africa. 



The sociologic unities have been studied so far only in very 

 few localities. From British Guiana we have a good detailed 

 study by Davis and Richards. They distinguish five consocia- 

 tions. While in general in tropical forests the normal condition 

 is that no one single species reaches plain dominance, four of 

 these types have a dominant and only one follows clearly the 

 plan of mixture. The Mora forest dominated by the strongly 

 buttressed Mora excelsa occupies the lowest ground. It forms 

 a broad strip along both banks of the Moraballi Creek and along 

 the branch creeks. On the lower slopes of the smaller flat- 

 topped hills lives the Morabukea forest type dominated by Mora 

 gonggrijpii. This is much the darkest type of forest. The lower 

 hilly land is covered by the mixed-forest association. Many 



