E. Joi-gensen. 



According to Gran's theory, the foreign arctic forms must be 

 considered to come from the resting- spores which have been de- 

 posited, and so must not be looked upon as foreign, but as species 

 which now on our coasts have an unusually short period of vege- 

 tation in the spring, remaining otherwise in rest at the bottom as 

 spores. 



It will clearly be seen, from the tables of the species which 

 have been found in the plankton here dealt with, that a large 

 number of foreign species occur during the period of the inflow, 

 par'tly being decidedly high arctic, at any rate as far as their di- 

 stribution is now known. Of such species, I would particularly 

 mention Th' I lassiosirahyalina, Fragilaria cylindriis, „NavicuIa" Van- 

 hoffeni, Coscinodiscus hioculatus, Pleurosigma Stuxhergi, Nitzschia 

 frigidu and Chætocerns fiircellatus. 



These two thmgs — the great uniformity and the foieign cha- 

 racter — taken in connection with each other seem to me most 

 natui-ally to give rise to the supposition that those species, which 

 foi'm the bulk of the plankton at the time when the masses of 

 diatoms appear, are brought in from the ocean by arctic water, 

 and that they are — perhaps by mixing with the waters of the 

 Atlantic — brought into better conditions of existence and there- 

 fore multiply by division. This way of generation will of itself — 

 that is to say when such division is not only the exception — 

 easily lead to production e n m a s s e, as one has good opportunities of 

 seeing during the development of diatoms, when artificially cultivated. 



What constitutes the improved conditions of existence, is another 

 question, and there is no reason foi' me to deal with this matter 

 here, as I have no observations to fall back upon, but there cannot 

 be very many factors to take into consideration. Gean supposes 

 that the rich supply of nourishment is its cause fcfr. the foregoing.) 



In this connection, I will only observe that froin his standpoint 

 Gran explains that the reason why the development of the large 

 masses stops of itself, and why the masses disappear, is that the 

 nourishing matter has been quickly used up. According to my 

 experience light plays an important part in the culture of diatoms, 

 their development being greatly assisted by a certain degree of light, 

 while a somewhat greater degree has precisely the opposite effect. 

 One might, therefore, perhaps find a reason in this fact for the 

 disappearance of the masses, in as much as long periods of sunshine 

 might destroy the assimilating powers of the chromatophores. 



It is highly probable that the phenomenon is due to botli these 

 causes. 



Tiiis disappearance of tiie masses of diatoms may, however, be 

 local, and be caused by the rushing in of other water (cfr. the con- 

 cluding remarks on the Baltic current.) 



I have called the phenomenon the inflow') of diatoms, partly 

 because it conveys the immediate impression of an inflow from out- 

 side, and partly because I really consider that it is caused by the 

 lu'inging in of foreign forms. It is, however, only necessary to consider 

 that the germs for the evolution of the masses of diatoms are thus 

 brought in, whether it be light, temperature, nourishing matter, or 

 most likely all three factors combined, which further their deve- 

 lopment. 



As already mentioned, the southern inflow appears always to 

 contain some species which arc not found in the northern, so it 

 would seem likely that the western coast of Norway partly receives 



1) It is useful in the remarlvs i 

 natu this period. 



a sjjecial name to desig- 



water from anothei' (juarter than the northern coast. Gran appar- 

 ently considers Stadt to be the bouudary lino for some of the cha- 

 racteristic species. 



This, I think, makes it clear, that it is of some importance 

 to tiy to discover whether there is really any variation or not year 

 after year in the species found in the inflow of diatoms. On the 

 whole, it seems to me that the great difference of, and changes in 

 the interpretation of the plankton at least show that it has not yet 

 been sufficiently studied to make any quite reliable basis for hydi'O- 

 graphical conclusions. 



As is the case with the majoiity of biological phenomena, the 

 development and changes in plankton are of such a complicated 

 character that a knowledge of many factors which work together, 

 and which as yet we are partly quite unacquainted with, is neces- 

 sary, so that to get a clearer conception and better knowledge of 

 the many remarkable phenomena, which are to be found in our 

 coast plankton alone, will give enough work for many years. 



Before I leave this subject, I think I ought to better explain 

 my position with regard to the hypothesis of resting spores, which 

 at first sight, it must be confessed, seems to give an attractive 

 explanation of many phenomena. 



When Gean considers the neritic species to be characteiized 

 by resting spores, in contradiction to the oceanic species which 

 have none, this distinction seems to me in a sense to follow of 

 itself, but contains no proof of the „over summering", by resting 

 spores on the bottom. I look upon these spores as a means by 

 which the individual diatom attempts to escape from unfavourable 

 surroundings, as the specific weight increases. So far, I agree 

 with Gean. His supposition that they often sink to the bottom is 

 doubtless also correct in very many cases, in fact I think this is 

 finally most often their fate in the coast water. But I think it 

 is just as certain, in the majority of cases, that the individual to 

 begin with is only forced into underlying water of a greater specific 

 weight. What its further fate will be, depends entirely upon cir- 

 cumstances. If it thrives, it will live on, and possibly multiply. 

 If, however, it does not tlnive, the tinai result will be that it 

 reaches the bottom. Then, as a rule, it will be altogether played 

 out, at the most, it niiglit be included in a preparation of bottom 

 material. 



In an earlier paper (L. 92) I have suggested that the thick- 

 ening of the horns in certain Chætoceræ (e. g. C. conroUihis, C. eon- 

 turtus and many others) might be a biological phenomenon corre- 

 sponding to the formation of resting spores, although the latter are 

 undeniably more ett'ective. 



In his last work. Gran also mentions (L. 7(), p. 129—130) 

 numerous dead cells and resting spores tVom a deep water sample 

 (The Stor Fiord, Søndmøre, stat. 3, 200—530 m.), these consisting 

 partly of species which had disappeared from the surface. How 

 these could — even if they remained alive — again come up from 

 such great depths, is really difficult to explain, unless too arbitrary 

 suppositions be resorted to. Besides, the greater depth, imphes 

 little light, but light is an absolute condition of vital importance 

 for the diatoms. The fact that bottom samples from deeper than 

 50 m.s show a very poor diatom life, is very instructive in this 

 connection; while a very rich diatom flora may be found at lesser 

 depths. At depths of under 100 m.s the bottom flora of diatoms 

 consist only of empty valves of pelagic species plus some other 

 matter, also a few diatom valves, which has been washed down 

 from the shore and here too resting spores are found in varying 



