90 



In considering the relation ol" the i'requencj of thèse Diatoms 

 to a suitable substratum, it will be convenient to take the two 

 together in the first place, *. e. to consider the epiphytic Dia- 

 toms as a whole; for, apart from March and April of 1908, when 

 Achnanthes minutissima occurred in some slight amount, ail 

 the other epiphytic Diatoms are so scantily represented, as to 

 be quite negligible. The chief snbstrata on which thèse epi- 

 phytes are found are furnished by Lemna, Oedogonium, 

 Microspora and Conferva. Lemna is generally rather scanty 

 in amount until April or May, so that its importance as a substra- 

 tum during the period of frequency of the two epiphytes is not 

 very great. On the other hand considérable quantifies of the 

 three fllamentous forms are found during the first four months 

 of the year, and the degree of abundance of the epiphytic Dia- 

 toms appears to bear a direct relation to the extent of develop- 

 ment of the fllamentous Algae. A comparison of the frequency 

 table of Synedra radians and Eunotia lunaris in the early 

 months of 1907, 1908 and 1909 with the chart on p. 66 fully bears 

 this out, but the matter is more directly apparent from the table 

 on the next page. Taking the values for the différent symbols 

 given on p. 83 the total amounts of Microspora, Oedogonium 

 and Conferva for each month hâve been added together for the 

 months from January to June inclusive ; the symbols placed 

 below thèse numbers show the combinée! représentation of the 

 two epiphytic Diatoms in the différent months. It will be seen 

 that the maxima of the epiphytic Diatoms in each year corresponds 

 to the maximum spring-growth of the filamentous Algae in that 

 year. Complète correspondence of thèse figures is of course 

 not to be expected, since they are only rough approximations. 

 Turning now to consider the individual représentation of the 

 two epiphytes, it will be noticeel that Synedra radians exhi- 

 bited a pronounced maximum only in 1906 and 1908, Euno- 

 tia lunaris only in 1907 and 1908. An examination of the 

 chart on p. 66 and of the tables from which this is constructed 

 shows that in 1906 and 1908 Conferva w T as more important in 

 the early months of the year that in 1907 or 1909, whilst both 

 in 1907 and 1908 Microspora attained a maximum at this time. 

 The very abundant Synedra radians of March and April 1906 

 was observed principally on Conferva (1) , while the fréquent 



(1) Attention may be drawn to the l'act that Synedra radians was not 

 observed on Microspora in Abbot's Pool (Fritsch and Rich, 1909, p. 51). 



