April 2, 1874] 



NA TURE 



423 



Fertilisation of the Fumariacese 



The accompanying note has been given me by my friend Mr. 

 J. Traherne Moggridge, and I should feel obliged if you would 

 insert it in Nature with the view of eliciting the communication 

 both of other similar phenomena, and of some explanation of 

 them. St. George Mivart 



Mentone, March iS 



Nolc on apparently ttseless Colouring in the Flowers of a Fumitory 

 {Fumaria capreolata var. pallidijiora, F. pallidiflara Jord. ) 

 I observe that in this plant at Mentone the flowers attain their 

 brightest colouring after the ovaries are set, and when fertilisa- 

 tion is no longer necessary, or indeed possible. During the 

 period previous to impregnation, the flowers are pale and nearly 

 white, and the pedicels erect or horizontal ; afterwards they be- 

 come pink, or even crimson, and the pedicels are recurved, and 

 the colour ot the petals, which retain their form and position 

 ntil the ovary has nearly attained its full size, intensifies with 

 the lapse of time. 



If the reverse had been the case there is little doubt that we 

 should have regarded the bright colouring as specially adapted to 

 attract insects, and as existing for that purpose, insects being, 

 according to Prof F. Hildebrand, * important agents in the fer- 

 tilisation of fumitories ; but here, as the brigiter flowers are 

 those which no longer need or are capable of profiting by the 

 interference of insects, this explanation ceases to be possible. 



This little fact, therefore, would seem to be one which might 

 be classed with those which teach us that, side by side with the 

 developments and modifications which are plainly beneftcial to 

 the organism of which they form a part, there are others, which, 

 as far as we can see, are neither useful nor harmful to their pcs- 

 sessor, though they may, and frequently do, supply features 

 which especially attract our attention and admiration. 



J. Tkaherne Moggridge 



OCEAN CURRENTS 



TWO papers which Mr. CroU has recently published 

 " On the Physical Cause of Ocean Currents " {Pliilo- 

 sophical A/aga::iiu- for Feb. and Mar. 1874), bring the main 

 question at issue between him and myself into very dis- 

 tinct view ; and as the results of the Challenger Tem- 

 perature-survey of the Atlantic, lately made public by the 

 Admiralty, afford (as it seems to me) important data 

 towards the settlement of this question I shall be glad 

 to be allowed to point out what seem to me their chief 

 bearings upon it. 



The position taken by Mr. CroU is, that all the great 

 movements of ocean-water, deep as well as superficial, 

 depend on the action of winds upon its surface. And 

 whilst freely admitting that Polar water finds its way 

 along the floor of the great ocean-basins into the equa- 

 torial area, he affirms that this is merely the reflux of the 

 current which has been driven into the Polar basins by 

 the agency of winds. 



On the other hand, it is fully recognised by myself, 

 that the current movements of siir/ace-waXex are, for 

 the inost part, produced by the agency of winds ; but 

 these movements, I contend, all belong to a horizontal 

 circulation, which lends to complete itself, — a surface in- 

 draught being produced wherever a surface outflow is 

 kept up, as we see in the horizontal circulations of the 

 North and South Atlantic, the North and South Pacific, 

 and the Indian Ocean, depicted in Mr. CroU's own map. 

 But I maintain that the deep movements of ocean-water 

 are the result of a vertical circulation, which is main- 

 tained by the continuance of a disturbed equilibrium 

 between the Polar and equatorial columns, occasioned 

 by the surface-action of Polar cold and equatorial heat. 



As Mr. Croll is unable to understand why 1 should 

 speak of Polar cold, rather than equatorial heat, as the 

 primiim mobile of this vertical circulation, and accuses 

 me of an ignorance of the fundamental principles of 



* " Ueber die Bestaubungsvorriclitiuigen bei den Fuinariaceen,"in Prings- 

 heim's " Jahrbucher," vol. vii. part 4, p. 423 (1870). Reviewed in " Bull. 

 Soc. Bot. de France," xix. (1872), p. 145. 



physics in so regarding it, I may be allowed first briefly 

 to explain myself; since others may experience the same 

 difficulty, from some want of precision on my part in 

 stating my case. The eminent physicists, however, with 

 whom I have had the advantage of discussing this point, 

 do not share Mr. CroU's objection, but hold my statement 

 to be perfectly correct. 



Heat applied to the sttrface ol any body of fresh 

 water, whether by solar radiation, or by the experimental 

 application of a heated plate, will raise the temperature 

 of the stirfacc-film, without producing any downward 

 convection. Limited downward convection, however, is 

 occasioned in salt water by the sinking of the surface- 

 films which are concentrated by evaporation ; but this con- 

 vection 1 found in my Mediterranean observations, which 

 have been fully confirmed by those of the Challenger in the 

 equatorial area, to be practically limited to the first fifty 

 fathoms. Water in a long trough may thus be super- 

 ficially heated (as I have experimentally ascertained), by 

 the application of surface-heat to one-sixth of its length, 

 until the temperature of its whole surface-film is raised 

 to 100" or more ; but the further application of sur- 

 face-heat expends itself in vaporisation, and does not 

 communicate itself in any sensible degree to the mass of 

 water beneath, which, therefore, can not be put in motion 

 by such application. On the other hand, the moment that 

 snrface-cold is applied, a downward convection is pro- 

 duced, as Mr. Croll may easily ascertain for himself if 

 he will only try the expernnent ; and the continued appli- 

 cation of such surface-cold to any one portion of the 

 surface will maintain a constant movement through the 

 entire mass of the liquid, until thermal equilibrium is 

 restored by the cooling-down of the whole. But if the 

 restoration of this thermal equilibrium be prevented by 

 the application of heal to another part of the surface, the 

 disturbance of equflibrium will be kept up, and a vertica 

 circulation maintained, as long as these two opposing 

 agencies are in operation. If Mr. Croll cannot see that 

 this must be the case, I am not responsible for his failure 

 to apprehend that which theory and experiment alike 

 sanction. 



I re-affirm, then, that cold applied to the surface has 

 exactly the same motor power as heat applied at the 

 bottom ; and that its motor agency is more potent than 

 that of heat applied at the surface, simply because the 

 former is diffused by convection through the entire mass 

 of the water, which it keeps on cooling and moving, 

 whilst the latter is limited to the surface-film, and expends 

 itself in producing evaporation. 



Mr. Croll objects to this, that, if it were true, nearly 

 the whole mass of oceanic water must have an almost 

 Polar temperature. I accept this issue ; and refer to the 

 Challenger temperature-soundings, as justifying it. If 

 he will look at the section taken across the equator, he 

 will find that — as I had predicted — Polar water there lies 

 within a very short distance from the surface. At less than 

 100 fathoms' depth, the temperature falls from 78" at the 

 surface to 55°, and the isotherm of 40° is reached at about 

 320 fathoms. Below this lies a stratum of more than 

 2,000 fathoms Jhic.'cncss, whose temperature, ranging 

 downwards from 40' to 32"'4, shows it to consist mainly 

 of Polar water. And as, from the data supplied by the 

 Mediterranean and Gulf of Suez temperature-soundings, 

 a body of equatorial water secluded from all connection 

 with the oceanic circulation might be expected to have 

 the uniform (or isocheimal) temperature of 75° from 50 

 fathoms downwards, it is cle.ir that the influence of Polar 

 cold here extends itself upwards within 100 fathoms of 

 the surface. 



Again, Mr. Croll says that I have made no allowance 

 for the excess of salinity in equatorial water, which, 

 according to him, must counterbalance the increase of 

 specific gravity produced in Polar water by the reduc- 

 tion of its temperature. Here, again, he is unfortunate 



