88 THE AQUATIC GARDEN. 



this pretty and interesting plant is derived from the 

 presence of certain little bladders attached to the 

 thread-like leaves (a). These fill with air, and buoy up 

 the flower-stalks above the water. After fertilisation 

 has been effected they fill with water, and thus the 

 entire plant sinks so that the seeds can be ripened at 

 the bottom. The bladder-wort is therefore one of 

 the most interesting of all our aquatic plants, whilst 

 its yellow flowers appear very prominent amidst the 

 whitish or pinkish tints which our British aquatic 

 flowers are usually adorned with. 



Villarsia nymphceoides is a much rarer plant than 

 many of the above mentioned, but it is an exquisite 

 object, and may no doubt be obtained living from 

 London dealers. ' It is a British plant, inhabiting 

 ponds as a rule, and is also found in the Thames. 

 The leaves are round, and float on the top of the 

 water ; whilst the largish yellow flowers are borne on 

 single stalks. Trapa natans, although not a British 

 plant, is easily procurable ; as it is found abundantly 

 in many European streams and rivers. Its flowers 

 are whitish, tinged with red, and the leaves grow in 

 very elegant semi-floating clusters. We have already 

 referred to the ubiquitous pond weeds (Lemna) as 

 forming a fresh, green covering for small aquaria. It 

 is not wise to cultivate this plant too much, as it 

 gives a rather poverty-stricken look to the whole 

 tank. Among other plants which are useful for 

 oxygenating purposes we may mention the water 



