420 



Ecology 



and in the Antarctic continent it forms a veritable carpet on the sloping 

 ground below the penguin rookeries (W. & G. S. W., '11). 



4. Leaf- and bark-epiphytes. Prominent amongst these is the genus 

 Trentepohlia, the abundant presence of which depends entirely upon rainfall. 

 There are many species of the genus, about two-thirds of the number being 



Fig. 266. Phytophysa Treubii Weber van Bosse. A, stem of Pilea (wf) with pustules (pu) 

 caused by algal parasite; B, section through part of one of the galls showing four of the 

 flask-shaped cttnocytes (az) of the Alga with their necks (ha) projecting outwards ; C, algal 

 ccenocyte during spore-formation; /, nuclei; m, wall of ccfinocyte; sp, aplanospores ; st, 

 sterile cells ; ;/', some of the surrounding culls of the host-plant ; D, two aplanospores ; 

 chr, chromatophore ; k, nucleus. A, nat. size ; B, xBQ ; C, x 49 ; D, x about 700. (After 

 A. Weber van Bosse, from Wille.) 



tropical epiphytes, and it is in the damp tropical woodland areas that species 

 of Trentepohlia attain their greatest luxuriance. In temperate countries 

 they are frequent in those districts with an annual rainfall of upwards of 

 40 inches. In western Europe several species occur on the trunks and 

 branches of trees in woodlands at no considerable altitude. It is a curious 

 fact, however, that T. aurea, which is much the commonest species in the 



