40 



( 'allitriche vcrna is also always présent in some quantity, but 

 becomes rather crowded ont by other i'orms during the summer. 

 Ranunculus aquatilis becomes more and more abundant 

 during the early months of the year, especially in the deeper parts 

 of the pond, and is in full nower in April and May; tins period 

 marks the first phase in the Phanerogamic tiora of the pond. 

 Soon after May a great part of the Ranunculus dies away, and 

 it is not strongly representcd in the second half of the year until 

 October or November. About April Glyceria fluitans puts in 

 an appearance, and later in the same month numerous seedlings 

 of Bidens cernua arise near the marshy edges of the pond. 

 Juncus arMculatus also appears in April and subsequently 

 (in the summer) exhibits a very vigorous growth, while around 

 the edge ./. conglomeratus and /. infleocus appear. In June 

 the whole surface of the pond is typically covered with Lemna 

 and mat-like masses of Bidens-seedlings. Later in the same 

 month the Glyceria and the rushes corne into nower. A third 

 phase in the Phanerogamic flora is reached in the middle of 

 July, when Glyceria fluitans constituées the predominating 

 feature. Together with Juncus conglomeratus and Bidens 

 cernua it forms a screen over the central parts of the pond. 

 In August the Bidens is in full nower and often occupies nearly 

 the whole of the pond, especially when the latter dries up. Soon 

 after flowering the Bidens dies away, and Lénine wi'h some 

 Ranunculus aquatilis and Callitriche verna again become 

 conspicuous. By November the Lemna is diminishing in 

 amount. while Ranunculus aquatilis bas increased. 



The Phanerogamic végétation of the pond thus normally 

 shows the following phases : 



I. Spring-phase : Ranunculus aquatilis dominant. 



II. Early summer-phase : Lemna and Bidens-seeàlmgs. 



III. Summer phase : Glyceria fluitans dominant; rushes, 

 Bidens. 



IV. Laie summer-phase : Bidens cernua dominant. 



V. Autumn-phase : Lemna, Ranunculus aqua/ilis, 

 Callitriche verna. 



VI. Winter-phase : Ranunculus, Callitriche. 



It will be seen that during the warmer period of the year 

 (from the beginning of April till the end of < H-(ober) a large part 

 of the surface of the pond is occupied by Phanerogamous a^uatics 



