CHAPTER XI 



PLANTS FOR THE AQUARIUM 



I. Algae, marine and freshwater Although some of the 

 mosses grow submerged, and also a few members of the fern 

 alliance, yet in the general case it may be said that aquatic 

 plants are either algae or flowering plants. These two groups 

 have, however, a very varying degree of importance, from the 

 aquarium-keeper's point of view, in fresh and salt water. With 

 the exception of Zostera, the plants available for the marine 

 aquarium may be said to be algae only, for the plants of salt 

 marshes are not suitable for the ordinary saltwater tank. On 

 the other hand, as in fresh water a considerable number of 

 flowering plants are available, the freshwater algae, with the 

 exception perhaps of the interesting Chara and its allies, can be 

 neglected. Their beauties in any case are not those that appeal 

 to the unaided eye, and the flowering plants are much more 

 interesting. We need, therefore, here only speak of Chara and 

 of a few of the marine algae. 



A few words may first be said as to algae in general. As a group 

 they vary greatly in size. A vast number are microscopic, while 

 others, especially the marine forms, reach sometimes a great 

 size, and considerable external differentiation of form, although 

 they are internally of great simplicity. Without stopping to 

 give any exact account of their peculiarities, we may note that 

 they do not, like higher plants, possess fibre-vascular bundles. 

 This means that if we tear across, for example, a frond of bladder-- 

 wrack, we do not find those stringy threads, consisting of food- 

 carrying tubes, which are to be found in a flowering plant or 

 fern, as for example in a fern-rootstock, or in the stalk of a 

 hyacinth. Again, although forms like bladder-wrack, for example, 

 or the beautiful red Delesseria, so often cast up on the shore, 



or Bryopsis plumosa, may to some extent mimic in appearance 



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