500 



NA TURE 



[March 22, 1906 



plankton and the remaining flora and fauna of our waters 

 lies in the fact that all the organisms which compose 

 it are free-floating during the greater part of their life. 

 Practically all the pelagic plants belong to the group of the 

 alga;, and their minute size, of course, suits them well to 

 a floating existence. A certain number of them are motile 

 (e.g. Volvox, Gonium, Pandorina, &c), and these are able 

 actively to maintain themselves in their position in the 

 water ; but the large majority are non-motile, and all 

 these forms are slightly heavier than water, and conse- 

 quently tend to sink ; they develop diverse mechanisms, by 

 means of which their power of flotation is increased. The 

 most important of these are : — assumption of a flat plate- 

 like shape (Pediastrum, Merismopedia, many Desmids) ; 

 development of numerous delicate processes from the body 

 of the plant (Stephanodiscus, Richteriella) ; arrangement 

 of the individuals of a colony in a more or less stellate 

 manner (Asterionella, some Tabellarias) ; assumption of a 

 delicate acicular shape (Synedra) ; formation of fat in the 

 cell (many Diatoms and Cyanophycea;), and so on. 



In spite of these adaptations, however, most of the non- 

 motile organisms of the plankton sink to the bottom of 

 the containing vessel in the space of a few minutes after 

 they have been collected. How is it that this does not 

 happen in nature? It has been suggested that the con- 

 tinuous currents in the water, due to the wind and other 

 causes, help to buoy up the organisms of the plankton ; 

 but it is of course also possible that in collecting such 

 delicate forms they are damaged in some way or other 

 so as to deprive them of that power of floating which 

 suits them so well to their natural habitat. An interest- 

 ing point connected with the development of the diverse 

 floating mechanisms is that in some plants they have been 

 found to be far more strongly developed in the summer 

 than in the winter forms ; this is, undoubtedly, in some 

 way connected with the lower specific gravity of the water 

 in summer, although the exact relation is not yet quite 

 evident. 



If the plankton of any piece of water is examined from 

 week to week or month to month, we find not only 

 astonishing variations in the quantity of organisms pre- 

 sent, but also very marked differences in the specific con- 

 stitution of the pelagic life. The quantity of the plankton 

 is generally very much less in the winter than in the 

 summer months, and the organisms composing it are quite 

 different in the two seasons. Thus in the Thames there 

 are four well marked annual phases, each characterised 

 by its own peculiar plankton. This periodicity exhibited 

 by the pelagic life stands in close relation to the external 

 seasonal changes ; some of the forms prefer cold, others 

 warm water, and consequently they flourish in those 

 seasons which are most to their liking. Some plants are 

 particularly sensitive, and consequently only put in an 

 appearance for a very short space of time each year. 

 During their period of absence from the plankton these 

 organisms persist as resting spores in the mud at the 

 bottom of the piece of water ; when favourable conditions 

 return the spores germinate, giving rise to a new gener- 

 ation of pelagic organisms, which by their prolific division 

 are able to dominate completely a piece of water in a few 

 days' time. 



The pelagic plants form the food of the animal plankton ; 

 these, again, are devoured by their larger brethren, which 

 are the main source of nutrition for the smaller fishes. 

 The larger fish are mostly carnivorous, feeding on smaller 

 individuals of their kind. The organic matter of the 

 pelagic plants thus gradually travels from one organism to 

 another until it comes to form part of the body of the 

 large aquatic animals ; it passes through a series of in- 

 carnations before being returned to the water in the form 

 of excrements or products of decay of dead animal and 

 vegetable bodies. This organic matter is built up by the 

 pelagic plants from simple inorganic salts and from carbon 

 dioxide dissolved in the water, and these latter substances 

 are thus changed into a form which makes them available 

 to the aquatic fauna. All the organisms of the latter, as, 

 indeed, all the animals of the world, are ultimately 

 herbivorous. Without some kind of plant growth a piece 

 of water must remain a lifeless, dead mass, unpopulated, 

 and a thing apart from the living world around it. The 

 NO. 1899, VOL. J?,~\ 



presence of vegetation immediately transforms it into a 

 throbbing universe, full of energetic life, exhibiting complex 

 inter-relationships, and connects it with the remaining 

 parts of our universe. The most important element of the 

 vegetation from this point of view, however, is the phyto- 

 plankton, and a piece of water with plenty of pelagic 

 plants is sure to form a good breeding-place for fish and 

 other aquatic animals. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Oxford. — The report of the committee of the school of 

 geography for 1905 shows that the school now holds a 

 strong position in the University, and is doing valuable 

 work in encouraging the study of geography and surveying, 

 and in providing special courses of geographical lectures 

 suited to the requirements of the different final honour 

 schools. Both the lectures and practical instruction were 

 well attended throughout the year, although there were only 

 a few candidates for the diploma. This year, in addition 

 to the ordinary work during term, a special course lasting 

 three weeks, specially suited to those who are engaged in 

 teaching, is being arranged for August. The instruction 

 will be both practical and theoretical, and there ought to 

 be no lack of support for so useful an innovation. 



Cambridge. — The forestry committee having been com- 

 missioned to submit a scheme of study and examination 

 for the diploma in forestry, recommends that the Senate 

 approve the following : — Candidates, before receiving the 

 diploma in forestry, shall be required to produce evidence 

 that they have (1) passed (or obtained exemption from) the 

 Previous examination, together with the additional subjects ; 

 (2) satisfied the examiners in physics, chemistry, geology, 

 and botany, either in part i. of the examination for the 

 diploma in agriculture, or in that examination in combin- 

 ation with the Natural Sciences Tripos, part i., or in some 

 other examination or examinations approved by the com- 

 mittee ; (3) diligently attended courses of instruction in 

 forest botany, in entomology, in forestry, in forest men- 

 suration, surveying, and engineering, and such other courses 

 in related subjects as may from time to time be approved 

 by the committee ; (4) attended for a time equivalent to 

 one academical year courses of instruction in practical 

 forestry approved by the committee ; (5) obtained a certifi- 

 cate of proficiency in practical forestry approved by the 

 committee ; (6) passed the examination for the diploma ; 

 (7) been admitted to a degree in the University. 



The general board of studies has approved for the degree 

 of Doctor in Science Mr. G. H. F. Nuttall, Christ's 

 College. 



The general board of studies also recommends that it 

 be authorised to appoint, subject to confirmation by the 

 special board for medicine, Mr. G. H. F. Nuttall to be 

 reader in hygiene in connection with the special board for 

 medicine ; that the university lectureship in bacteriology 

 and preventive medicine terminate on his appointment as 

 reader ; and that the readership terminate with the tenure 

 of office of Mr. Nuttall. 



Dr. W. A. Thornton has been appointed to the newly- 

 created professorship of electrical engineering at Armstrong 

 College, Newcastle. 



According to a message from Wolfville, Nova Scotia, 

 Mr. Carnegie has promised to the Acadia University 6000J. 

 for a new science building as soon as 20,000/. has been 

 raised for a forward movement now in progress. Of this 

 sum nearly half is already in hand, and the rest is de- 

 finitely promised. 



The council and principal of the Bedford College for 

 Women will hold the usual reception at the college on 

 Commemoration Day, May 9, after the presentations for 

 degrees at the University of London. The Pfeiffer entrance 

 scholarship in science, tenable for three years, and of the 

 annual value of 48Z., will be offered for competition in 

 June next. 



At the annual dinner of the students of the Camborne 

 Mining School, held in Camborne on March 10, the prin- 



