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SO that one might be led to consider it a variety. I think it 

 is a perfectly mature frond as regards size, as the plants dis- 

 appeared from the aquarium shortly after it was collected. 

 The plant may, moreover, develope better on the smooth glass 

 than on the rougher stems of water plants ; in fact, it is just 

 one of those conditions that might fairly be supposed to give 

 rise to a variety. 



