Smith: Notes on tlic Vegetation of Ponds. 393 



occupies the deepest part of the pond. In consequence of the 

 eccentric position of the Pondweed the zones of Bur-reed and 

 Dropwort are narrow at the northern end, but they are sharply 

 defined. Towards the southern end both plants lose their 

 zonal arrang"ement, and form masses extending across the pond. 

 The Dropwort, however, is always nearer the shore than the 

 Bur-reed. It may, therefore, be inferred that the Bur-reed 

 prefers deeper water than the Dropwort ; this was also the case 

 in PMg-. I. The Water Plantain is an interesting- plant in this 

 pond. It does not form masses like the other plants, but occurs 

 sing-ly amongst the Dropwort and the Bur-reed. In other 

 words, the Water Plantain is not a social species, whereas the 

 other plants shown are social. It is a feature of social species 

 of plants that they can g^row closely tog-ether as a mass, and 

 hold their own more or less completely against all comers. 

 One can appreciate this in the case of the Pondweed, with its 

 broad floating leaves lying- edg-e to edge, or overlapping, so as 

 to occupy the whole surface and shade the bottom, thus checking- 

 the g-rowth of other plants which may try to grow below them. 

 Amongst trees, the Beech is one of the best examples of this 

 kind of social plant. The Dropwort, Bur-reed, and Rushes are 

 also social plants, and it is noteworthy that their long, slender, 

 erect leaves are similar in form to the grasses which on land are 

 amongst the most successful of our social plants. Just as the 

 grasses, with their closely interwoven roots and stems under- 

 ground, and their close, erect, leafy shoots aboveground, can 

 keep in check the growth of other plants and maintain a close 

 sward, so in our pond the Dropwort, Bur-reed, and Rushes 

 maintain themselves in distinct zones with little mixture. The 

 Dropwort is not quite so successful as the other two, and 

 amongst it plants of Water Plantain have found a place and 

 have also succeeded in gaining ground in the closer Bur-reed 

 zone. Turning now to the Rushes on the margin. The Rushes 

 form a close well-marked zone, which at the time of our visit 

 was standing in water and therefore formed part of the pond- 

 vegetation. Out of the water there was, however, no scarcity 

 of Rushes, and from general experience most of us would 

 regard the Rushes as plants of the marsh rather than water- 

 plants. The Rush zone of this pond therefore indicates that 

 part of the margin which is only occasionally under water, and 

 is generally marsh. From this one may infer that this pond, as 

 a rule, contains less water than when we saw it. It has a 

 maximum depth which is determined by the sill of the outflow 



1903 October i. 



