PLANT LIFE IN PONDS & STREAMS 



give it here, in Professor F. W. Keeble's Vlant 

 Animals, one of the excellent Cambridge Manuals 

 of Science. The fact is that the demarcation be- 

 tween plants and animals, low in the scale of 

 development, is not nearly so pronounced as it is 

 amongst the higher forms of life. Amongst the 

 plants of our pond we shall find that, like the land 

 plants, most of them are green, and many of them 

 are thread-like, so that the task of distinguishing 

 one from another may appear difficult. Examined 

 with the naked eye, many of them appear remark- 

 ably similar to one another; under the microscope 

 the differences are obvious. 



One of the most remarkable of the commoner pond 

 plants is known as Oscillatoria ; it does not boast 

 of a popular name but its scientific name is not very 

 difficult to remember after we have witnessed its 

 oscillations. Oscillatoria is a plant with particularly 

 animal-like movements. It is merely a thread, usually 

 green-blue * in colour, but sometimes red or violet. 

 The threads are never branched and, except when 

 in motion, are straight. Under a moderately high 

 magnification we can see that this thread-like plant 

 is not composed of a single cell but that it consists 

 of a number of cells, placed end to end. Sometimes 

 a few of these cells will break away and start life 

 on their own account. 



Whatever interest the structure of Oscillatoria 

 may have for us, we cannot help being struck with 

 its movements, and we must make a point of 

 observing them. The movement is j)eculiar and not 



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