Jan. 6, 1876] 



NA TURE 



191 



of excess of food, or some other casualty coming into the 

 category of possible accidents, may be invaluable. The 

 influx of air can always be regulated, or even stopped, 

 while an insufficient supply might be fatal, at least to the 

 more delicate animals. 



Let us now consider briefly the larger question, whether 

 vegetation ought to be admitted at all, and if so, under 

 what limitations and with what precautions. 



It is a proposition requiring no proof that the more 

 nearly the actual conditions of nature can be approached 

 in our tanks, the more likely is success to ensue, and the 

 more varied will be both the classes and species of animals 

 which it will be possible to domesticate and maintain in 

 health. 



An aquarium without seaweeds does indeed seem a 

 wide departure from this standard, and inasmuch as 

 vegetation fulfils the double function of naturally aerating 

 the water by absorbing carbonic acid and evolving oxygen, 

 and of affording wholesome and palatable food to tishes 

 and molluscs, its introduction would appear highly desir- 

 able if not attended with dangers more than sufficient to 

 counterbalance its advantages. On this point my friend 

 Mr. Hughes writes to me as follows in a recent letter : — 

 " I can no more see how fishes and molluscs can do with- 

 out vegetation than the higher primates without cabbages. 

 I feel certain that the mortality of fishes is due to its 

 absence in public aquaria. In my own tanks I have seen 

 a Blenny tugging at a mere rag of Ulva, black almost 

 with age, for half an hour, to get a mouthful of ' green 

 meat.' 



" Our most beautiful family of British fishes, the Wrasses, 

 haunt the banks of Zostera and Fucus ; and they do this 

 for more than mere play ! " 



The lovely tribe of Nudibranchs is practically excluded 

 at present by reason of the absence of their natural food, 

 the one or two species now admitted being animal feeders, 

 and by no means the most beautiful of their class. 



Why, then, are not seaweeds seen in the aquaria at 

 Brighton, Sydenham, or Paris ? 



I believe the answer to be this. For some reason they 

 do not appear spontaneously in the tanks of public 

 aquaria ; possibly because the water is deprived of all 

 germs of vegetation by the process of filtration or purifi- 

 cation to which it is subjected before use ; more probably 

 because, in order to secure purity, it is generally taken 

 from deep water, where such germs are likely to be 

 absent. 



Certain it is that in water taken from near shore and not 

 filtered, vegetation very speedily makes its appearance ; 

 and it is impossible to suppose that the gentle flow of 

 water in the aquarium could present any obstacle to the 

 development of germs which are no; prevented from find- 

 ing a resting-place and reproducing their species in every 

 rock-pool on shores washed by the tides and lashed by 

 the storms of the open Atlantic. 



As vegetation does not spring up spontaneously in the 

 tanks, and as the possibility of doing without it has been 

 practically demonstrated, its introduction has been 

 avoided because the growth of Algas is so rapid that they 

 are apt to become uncontrollable, to overgrow and hide 

 the animals from view, and at certain seasons by their 

 rapid decay to introduce into the tanks a large amount of 

 decomposing matter of the most objectionable kind— dif- 

 ficult to remove by oxidation, and likely to be fatal to 

 many of their delicate inmates. 



It cannot be doubted that the careless or indiscriminate 

 admission of vegetation into the marine aquarium is open 

 t© all these objections ; but, on the other hand, it seems 

 probable that its careful and judicious introduction would 

 be productive of excellent results to the health of the 

 animals, while there cannot be two opinions as to its 

 adding vastly to the charm of the whole scene. To 

 clothe, or partly to clothe, the bare and monotonous grey 

 apd yellow surfaces of rock which now form the regulation 



background of our tanks with'tufts of green and red sea- 

 weeds waving their delicate tresses in the gently-flowing 

 water, would add the one thing now wanting to make the 

 aquarium in practice what it is in theory, a miniature 

 reproduction of rock-pools and sea-caves. 



Now, the larger part of our British seaweeds are annual, 

 and perish rapidly in autumn and winter, after producing 

 countless zoospores from which a fresh generation of 

 plants is to be born in due time. 



These annual Algce would be dangerous inmates of an 

 aquarium, but in all three sections of the class (Rhodo- 

 spermeas, Melanospermeae, and Chlorospermeae) there are 

 perennial as well as annual species, and in the first 

 division the plants are usually of a more delicate nature 

 than in the two latter, of slower growth, and therefore 

 more manageable. 



We should therefore choose from among the Chloro- 

 spermeae the one or two species which alone are perennial 

 or biennial, such as Cladcphora arcta and Codium 

 tomentostitn. 



Unfortunately all the other species of Cladophora are 

 annual, as also are those of Enteromorpha and the lovely 

 Bryopsis piutnosa, which, however, might be tentatively 

 admitted by reason of its small size, slow growth, and 

 singular beauty. 



IJlva latissima, lactiisa and Unza are also all annual, 

 and should certainly be introduced very sparingly, if at 

 all, and with precautions designed to control and curtail 

 their growth, to which reference will presently be made. 



Among the Melanosperms scarcely any would be avail- 

 able. It is among the Rhodosperms that the ornaments 

 of the aquarium might be chiefly sought ; and although 

 experience would doubtless prove that some species of 

 this charming group would not flourish in confinement, 

 probably a sufficient number would be found, whose 

 graceful forms and attractive colouring would add im- 

 mensely to the beauty of the tanks, and which would yet 

 be sufficiently slow in growth to be under the necessary 

 controL 



What could exceed in elegance the waving fronds of 

 Ptilota plitmosa or the plaited tresses of Plocamiiiin 

 coccineum f 



What more delightful contrast could be imagined than 

 that of the white and pink somewhat rigid tufts of Coral- 

 Una officinalis mingling with the bronze-coloured leaves 

 of Chondrus crispiis ? 



What more charming juxtaposition than that of Geli- 

 dium cornutum, with its purple-black branches, the re- 

 gularity of whose sub-division almost suggests a metaUic 

 crystallisation, with the crimson ribbons of Delesseria 

 sangidnea, filmy almost to transparency ? 



Unfortunately the elegant Ceramiums are all annual, 

 but among such species as Rhodomela siibfusca, Polyides 

 rotundus, Polysiphonia fastigiata, Dasya coccinea, and a 

 score of others, all perennial and of moderate growth, 

 there is an abundant choice of variety in form, habit, and 

 colour, which would certainly justify the experiment of 

 setting apart one or two tanks in some public aquarium 

 for their trial. 



Were such an experiment to be [tried, fit would be 

 desirable to use ever}' precaution first of all to ensure a 

 clear field by the elimination, as far as possible, of all pre- 

 existing germs of other species than those which it is 

 proposed to cultivate ; a precaution, however, the necessity 

 of which the appearance of existing aquaria scarcely 

 suggests. 



Freshly gathered plants might then be introduced, in 

 all cases attached to pieces of rock or other base, which 

 would make it easy to remove them immediately if they 

 proved unsuitable for the purpose in question. 



If a large number of young plants made their appear- 

 ance on the sides or front of the tank, it would not be a 

 serious matter to run out the contents, scrub the surfaces 

 clean, refill it, and replace the original plants. 



