No. individuals/ mm.'^ 

 120 r 



100 



9 



/ \ 

 / \ 



MID-RIB \ 



to 



LU 



Q 



o 



Z 

 o^ 



uj 8 

 H 



■ r.rt-.rc.c.vc, 



APPROX. QUANTITY. 



PRESENT I 



2 



,r,rr,rc,C|VC, 

 I 2-5 4-5 10 13 15 cms. APPROX. QUANTITY OF INDIVID. 



DEPTH OF ALTERNATE LEAVES PRESENT 



Fig. 202 A, distribution of total epiphytes on successive leaves of 

 Oenanthe fluviatilis. B, C, distribution of Cocconeis placentula on 

 successive internodes of plants of Equisetum Itmosum, well separated 

 (3 stems average), r =less than 5 individuals per o-i sq. mm.; rr = 

 about 5 ; re = about 10 ; c = about 30 ; z;c = about 50. D, distribution of 



Cocconeis placentula ( ) and Eunotiapectinata ( ■) on crowded 



plants of Equisetum limosum (3 stems average). E, distribution of 



Stigeoclonium sp. ( ) and Coleochaete scutata ( ) on fairly 



crowded stems of Equisetum limosum (2 stems average). (After 



Godward.) 



same level. These maxima on the lower leaves are to be associated 

 with the diatom flora. It will also be observed that the number of 

 epiphytes on the internodes remains more or less constant, but 

 rapid growth of the substrate, e.g. the leaf lamina, tends to prevent 

 colonization by epiphytes. The density of epiphytes that are at- 

 tached to dead organic material is dependent upon the habitat of 

 the substrate, e.g. if it is floating then there are few epiphytes, if it 

 is attached or submerged the epiphytes are numerous, whilst if it is 

 lying on the bottom the epiphytes will be few. The various species 

 to be found are all a residuum from the last living state of the 

 material, and the assertion that dead material bears more epiphytes 

 than living does not appear to be correct in this case, and it can only 

 be supposed that it arose in the past through lack of quantitative 

 analysis. In some cases the appearance of epiphytes is due to change 



372 



