AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 5 1 



guished because the dissected leaves are not in an exact 

 circle around the stem: one is on one side, the next a 

 little further round and a little higher up, another still 

 further round and nearer the first, but still higher, 

 the whole forming a spiral arrangement which the bot- 

 anist calls alternate. 



Either of these plants is a specially good place for 

 attached diatoms (Chapter III). 



UTRICULArIA (Figs. 9 and 10). 



Of all our water-plants with finely divided leaves, 

 Utriculdria is probably the most interesting in itself 

 and one that can always be rec- 

 ognized at a glance. It is found 

 in long, somewhat branching 

 streamers, floating freely below 

 the surface or very slightly 

 rooted. A leaf of Utriculdria 

 vulgaris, a common species, is 

 shown somewhat enlarged in 

 Fig. 9, with the peculiar hollow 

 bladders, or "utricles," that dis- 

 tinguish it from all other plants, 



and give it one of its scientific Fig. 9.-A Leaf of UtrkuMria 



names. 



These utricles are almost always conspicuous when 

 the plant is taken from the water, as small, green, 

 semi-transparent particles attached to the leaves. 

 They are not unlike small pieces of jelly in appear- 

 ance, until examined with the microscope, when their 

 remarkable structure becomes apparent. Until within 

 a few years they were supposed to act as air-sacs to 

 keep the plant afloat. It was even said that they be- 



