Jtily 8, iSSoJ 



NA TV RE 



'17 



Thus Sachs is copied even to including the cyme in mono- 

 podial systems. Surely this is a contradiction in terms, 

 and might be avoided by the use of "lateral," in contra- 

 distinction to "dichotomous." In the figures (17, 19) of 

 uniparous cymes, Sachs, and with him Prantl, omit to 

 mention that the diagram is taken in plan, a point the 

 more important that in French and English text-books it 

 has been usual to give such diagrams of inflorescence in 

 elevation. Without noticing this, a trap is laid through 

 which not students alone have fallen into the error 

 of thinking that the Germans use "scorpioid" and 

 " helicoid " in senses inverse to the usage of other 

 botanists. Under inflorescence no mention is made of 

 the very useful French " Cymobotrya " terminology, 

 possibly through feelings of patriotism, with which, how- 

 ever, Englishmen are not concerned. The Elder is given 

 as the example of a cor_\mb ; which term is, however, 

 restricted by the best botanists to the corymbose raceme, 

 of which the elder is not an example. 



In the histology there are several not unimportant 

 errors, probably Prantl's own. He says that the phloem 

 contains both "phloem parenchyma" and " cambiform 

 tissue" — is not phloem parenchyma always (primitively 

 at least) cambiform ? We are told (p. 51) that the vessels 

 of secondary wood are "invariably provided with bordered 

 pits ; " this is far too absolute. Under collenchyma no 

 mention is made of its commoner form, distinguished as 

 "concave" by Vesque. Endoderm is defined as peculiar 

 to Dicotyledons ! Under " stomata " no mention is made 

 of water-pores. The account of the structure of roots 

 and the development of their secondary wood in Dico- 

 tyledons is hardly explicit enough, and almost demands 

 the introduction of one or two pure diagrams ; and when 

 it is stated that rootlets arise in front of the xylem 

 bundles of the root, mention should be made of such 

 important e.xceptions as Umbellifers and Grasses. 



The physiology proper is singularly well treated, though 

 perhaps with too great a fear of detail. Thus no suffi- 

 cient account is given of the vis a fronie and the vis a 

 iergo, which lead to the movements of the rising sap. 



A few httle mistakes have been left uncorrected in the 

 systematic part. The legume is stated on p. 197 to occur 

 in "all the LeguminosK;" and while this is modified in the 

 account of the order on pp. 27S-280, a true legume is here 

 implicitly denied to the Caesalpinieee ! "Replum" is given 

 as meaning a false-dissepiment of the Crucifers, a use 

 unauthorised by the best systematists, and inconsistent 

 alike with its application to the lomentaceous LeguminosK 

 and to its Latin signification. 



The figures are good, but, as usual in English editions 

 of foreign works, poorly printed. The worse fault of 

 separating them widely from the text they illustrate has 

 been avoided. 



Finally, despite all trouble taken by the editor, over- 

 sights will occur in a translation. Thus Tiillcn is given 

 in italics without its English (?) equivalent, "tyloses," 

 and "bracteole" is given instead of the more familiar 

 "bractlet." But these blemishes show how good is the 

 book in which they are the worst to be found ; they have 

 been here put forward chiefly in the hope of helping the 

 editor in the new edition which will soon be demanded; 

 and it is with a safe conscience that we would recommend 

 this book as the best of its kind in the English language. 



LETTERS TO THE EDITOR 



[ 77;;; Editor does not /told himself responsible for opinions expressed 

 by his eorrespondents. Neither can he mtdertake to return, or 

 to correspond with the writers of, rejected manuscripts, JVb 

 notice is taken of anonymous communications. 



\The Editor u?-gently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible othei~wise to ensure the appearance even of com- 

 mtinications containing interesting and novel facts.'l 



Ocean Circulation 



The notice in Nature (vol. xxii. p. 207) of the experimental 

 researches of Professors Haughton and E. Reynolds on the 

 coefficient of friction of water upon water, having concluded with 

 the statement that "the authors of this research point ont that 

 these results tend to negative the theoiy of Dr. Carpenter that 

 the phenomena of ocean-circulation are due to the greater height 

 of the water at the equator as compared with that at the poles," 

 I must be allowed to protest against being credited (or rather 

 (/Mcredited) with a doctrine which is neither expressed nor 

 implied in anything I have written on the subject. 



The doctrine which I have advocated is no other than that 

 first distinctly promulgated by Lenz in 1847, and now accepted 

 by numerous Physicists of the highest eminence, both British and 

 Continental; viz., that besides the horizontal ciiv.ulation produced 

 by the action of winds on the ocean-iurface, there is a vertical 

 circulation of which Polar cold is the primum mobile, consisting 

 of an underflow of Polar water (chiefly from the Antarctic area) 

 towards and even beyond the Equatorial zone, and a complemen- 

 tary ufipir-^crw of Equatorial water towards the Poles. 



That every part of tlie vast Oceanic basin in free communica- 

 tion with either of the Polar areas is occupied, to within the 

 range of the surface-heating produced by insolation, ^ by water 

 which has been cooled down in one of those areas, is now one 

 of the best-established facts of Terrestrial Physics. And those 

 who cannot find in the excess of specific gravity imparted to 

 sea-water by Polar cold, an adequate cause for this movement 

 of translation, are bound to account for it in some other way. 



I venture to submit to the accomplished professors of Trinity 

 College, that laboratory experiments made to determine the 

 friction of water upon water at sensible velocities can scarcely 

 prove that when the equilibrium of a great mass of water has 

 been distxirbed, there will not be any movement of translation 

 (however slow) for its recovery. And I would suggest to them 

 that they should rather investigate tlie conditions of one of those 

 "experiments ready prepared for us by Nature," which is 

 constantly going on in the Baltic Straits, and of which the 

 results have been for many years past most carefully recorded by 

 Dr. Meyer of Kiel and his associates. Four factors are there 

 in continually varying action, viz. (i) difference of level between 

 Baltic and North Sea water ; {2) difference of salinity ; (3) 

 difference of temperature, mainly due to an importation of Polar 

 water into the Skager-rack ; and (4) surface- mmemcnt produced 

 by wind, which may also modify the relative levels. 



I am assured by Dr. Meyer that the action of each of these 

 factors has now been so fully determined, that the effect of any 

 combination of them can be predicted as certainly as ordinary 

 tidal phenomena. And of the competence of small differences 

 in specific gravity to produce movement in gi'eat bodies of 

 water, no one who has investigated the question on the great 

 scale seems to have the smallest doubt. This was the un- 

 hesitating conviction of the late Mr. Froude, as the result of his 

 numerous obervations on harbours, lochs, and fiords, commiuii- 

 cating witli the sea at their mouths : for he assured me that 

 wherever the salinity of the water at their upper end is lowered 

 by the descent of fresh water from the land, producing a slight 



^ The re5earches of Prof Forel and his .i^sociates on the Swiss lakes 

 clearly show that m/resli water the heating eflect of insolation is limited to 

 about loo feet. In salt water, on the other hand— as I pointed out in my 

 Mediterranean Report — there is a dtrwirward convection of heat produced 

 by the sinking of the water made heavier at the surface by saline concentra- 

 tion. In the^Mediterranean, where this effect is limited to a part of the 

 year, it scarcely shows itself below loo fathoms (600 feel) ; but under the 

 Equator, where it is ccnstant. the surface-heated stratum ranges downwards 

 to from 300 to 400 fathoms. Beneath this depth the thermometer progres- 

 sively sinks in the ocean-basin generally (the thermal condition of the North 

 Atlantic Ijeing altogether exceptional) from 40° to 33° or thereabouts : whilst 

 in the Mediterranean, to the deeper part of whose basin the Polar under- 

 flo A' has no access, the thermometer shows a uniform temperature of from 

 540 to 560 (according to the locality) from the surface-heated stratum to the 

 deepest bottom (2,000 fathoms). 



