HARD WICKE 'S S CIENCE - G OSSIF. 



aquaria are those where the water never is changed, 

 but only circulated or aerated by some means, and 

 purified by growing vegetation. The same water 

 has remained in one of my tanks for fifteen, in 

 another for seventeen years ; yet in both it is now 

 absohitely clear and colourless. It would also be 

 interesting to hear of authentic cases of aquarium 

 animals dying of old agcy and to elicit opinions 

 whether death can be traced to other causes than 

 neglect, starvation, extremes of heat and cold, acci- 

 dent, casualties, and the like. 



Successful aquarium ■ keeping is no easy thing. 



and 3rd, I deprecate the waste and inefficiency ac- 

 cruing from a periodic change of water, adopted by 

 some aquarium-keepers. G. S. 



A FEW WORDS ABOUT FERNS,— THEIR 

 MANNER OF GROWTH, AND HOW 

 THEY MAY BE RAISED FROM SPORES. 



IT is generally known, I believe, that ferns do 

 not blossom like other ordinary wild flowers, 

 but are propagated by spores instead of seeds. The 



<-^., 





■^^.^^^^::M^k 



^^^ffmm -' I 



Mi S^^-C 







Fig. 4. Sharp-nosed Eel [Aiignina ncutiivsiris). 



requiring more patience and perseverance than 

 always falls to the lot of public companies or 

 private individuals. Many and great are the diffi- 

 culties and disappointments to be encountered. It 

 remains for each to think out these independently, 

 separately, and profit by the experience of others. I 

 am glad to see our editor, Mr. Taylor, has turned 

 his attention to this much-neglected subject, as shown 

 by the announcement of his book on "The Aquarium." 

 I advocate the following leading principles : ist, the 

 exclusion of limg-breathcrs ; 2nd, the system of uu- 

 changed zvater, purified by aeration and circulation ; 



spores are usually borne on the back or under-side o' 

 the frond, either in linear forms or irregular clusters. 

 These spores are simple microscopic cells, furnished, 

 like pollen-grains, with a double coat, and differ 

 from seeds in that they germinate from any point, 

 while the latter are restricted in their growth to two, 

 — viz. the radicle and the plumule, which develop 

 about the same time. From the germinating spore 

 first arises a small bud-like process, which, by cell- 

 division, soon produces a leaf-like expansion, termed 

 a prothallium. From the under part of the pro- 

 thallium filamentous rootlets are given off, and, mixed 



