470 



NATURE 



{March 29, 1877 



simplest means of transport." .... " Therefore the Coniferse 

 and Cicadite, no doubt, were anemophilous, like the existing spe- 

 cies of these groups." .... "A remarkable fact with respect to 

 anemophilous plants is that they are o'ten diclinous." For rea- 

 sons which he gives, Mr. Darwin considers that this "maybe 

 attributed to anemophilous plants having retained, in a greater 

 degree than the entomophilous, a primordial condition, in which 

 the sexes were separated and their mutual fertilisation effected 

 by means of the wind." . ..." If this view is correct, plants 

 must have been rendered hermaphrodites at a later though still 

 very early period, and entomophilous at a yet later period, 

 namely, after the development of winged insects." He subse- 

 quently points out, however, that "under changing conditions 

 of life .... some hermaphrodite plants, Hescended, as we 

 must believe, from aboriginally diclinous plants, have had their 

 sexes again separated ;" and he names as an example, Lychnis 

 dioica. It is only in the case of plants thus reverting that 

 dimorphism can be held to be a transitional stage. 



Prof. Thiselton Dyer, in his notice of Mr. Darwin's book in 

 Nature (vol. xv., p. 329), maintains an opposite view. "It 

 would not be difficult to show that all through the vegetable 

 kingdom the hermaphrodite condition precedes the dioecious." 

 Demurring to Mr. Darwin's conclusion that the monoedous con- 

 dition "is probably the first step towards hermaphroditism," 

 he considers it " not improbable that precisely the converse may 

 be more true." . . . . " To throw light on the question whether the 

 primordial plant was diclinous or not," he discusses the manner 

 in which it probably originated "from some plant-form not dis- 

 tantly related to Selaginella," and arrives at the conclusion that 

 tlie first flower would probably be extremely inconspicuous, 

 destitute of colour and hermaphrodite. 



How would it be, however, if, instead of regarding the spo- 

 rangiiferous cone or spike of Selaginella as the homologue of 

 a single flower, we compare it rather with the spike of Carex, 

 say, for example, C. pulka7'is ? The spike in this species is, 

 like the other, " composed essentially of an axis having modified 

 lateral appendages." The glumes of the sedge correspond to 

 the scales of the lycopod ; in the axils of the upper are found 

 the "male structures" — in Selaginella, sporangia containing 

 microspores j in Carex, anthers containing pollen ; in the axils 

 of the lower are found the "female structures" — in Selagi- 

 nella, sporangia containing macrospores ; in Carex, ovaries 

 containing each an ovule. There is then not even the differ- 

 ence that the position on the axis of the male and female struc- 

 tures is inverted. From C.ptdicaris, with its sirgle spike, the 

 passage is easy to species that have several spikelets, each male 

 at the top and ftmale below ; or to others that have the upper 

 spikelets wholly male, the lower ones wholly female. The same 

 arrangement ot male and female elements is found in Typha and 

 Sparganium, in most of the Araceas, to which order belong the 

 oldest fossil monocotyledons, and is preserved even in Sagittaria, 

 although in the last the flowers are of a much higher type, being 

 provided with petalloid perianths. So far as the comparison 

 with Selaginella is concerned, does it not favour the production 

 in the first place of unisexual flowers, at least as much as of 

 hermaphrodite? Thomas Comber 



Newton le Willows 



The Rocks of Charnwood Forest 



Some letters appeared in Nature a few months ago upon 

 the rocks of Charnwood Forest. In one of them it was sug- 

 gested that the syenitic bosses of Markfield and Groby might be 

 more ancient than the surrounding slates and grits. Some cf 

 jour readers may therefore be interested in learning that we have 

 now ascertained from unquestionable evidence in two places 

 that the syenite is intrusive in these rocks, and, as we believe, 

 in som.e of the highest and latest rocks of the series. We reserve 

 the details of the sections and localities for a paper which we 

 hope shortly to communicate to the .Geological Society. 



Sr. John's College, Cambridge, T. G. BoNNEY 



March 20 E. Hill 



Southern Double Stars 



Noting some queries in your November numbers (in the 

 "Astronomical Column") respecting some southern stars, I 

 inclose you some extracts from our occasional observations 

 that refer to the objects named in those and some previous 

 numbers : — 



Melbourne Observatory, January 22 



ROBT. L. J. Ellery 



Ship's Chronometers 



We have read with much pleasure your notice (vol. xv. p. 403) 

 of Sir William Thomson's lecture on Navigation, and are pre- 

 pared fully to endorse your remarks as to the value of Mr. 

 Ilartnup's system of rating ships' chronometers, by which 

 account is taken of the change of rate due to change of tem- 

 perature. 



It is but fair to mention, however, that the principle upon 

 which this system is founded was thoroughly investigated by 

 experiments upon a large number of chronometers by M. 

 Lieusous, of Paris, some thirty or forty years ago ; acting upon 

 his suggestions, and after independent investigation conducted 

 in our chronometer manufactory some six years ago, we pro- 

 duced a table for the use of captains and others using ships' 

 chronometers, which was fastened in the chronometer case, with 

 a small thermometer in front of it, in such a way that the top or 

 upper end of the column of mercury indicated, without any cal- 

 culation whatever, the mean rate that should be given every day 

 to the chronometer until some considerable change of tempera- 

 ture had taken place (say 3°), when the new position of the top 

 of the mercury column again showed the new rate to be used in 

 working the chronometer. 



We did not introduce this plan to the navigating public gene- 

 rally, as we feared that iufficient trouble (small though it actually 

 be) would not have been taken in the use of if, also for another 

 reason, i.e., nearly every chronometer that we have tested has 

 been found to require a difierent daily coefficient for a change of 

 temperature of ± i°, and ships rarely remain sufficient time in 

 port for us to determine this coeflScient after allowing for the time 

 necessary to clean the chronometer. 



But, as our system of tabulation may be of interest to your 

 readers and may possibly be available for other purposes, we 

 give it you as briefly as possible. 



From our experience (which agrees with that of Lieusous 

 and of Hartnup) we find that the ordinary compensation balance 

 without auxiliary, causes the chronometer to go at its fastest rate 

 (or in other words to lose least) at a point of the thermometric scale 

 somewhere between 55° and 70° F., usually at 60° or 65°, and 

 that from 25° to 30° above or below that "fastest point" the 

 chronometer loses or goes slower on its fastest rate by an amount 

 that is determined by multiplying the square of the difference in 

 temperature between the new point and the "fastest point" by 

 the coefficient of temperature for a change of 1° above or below 

 the "fastest point," i.e., by the amount that a chronometer 

 goes slower for having its temperature increased or diminished 

 by 1°. 



This is, however, only true so long as two conditions are^ 

 adhered to ; the first condition being that the "fastest point"] 

 (which can be moved at will by the chronometer maker), shall not 

 be taken outside the limits of 55° to 70", that is, the rule will 

 apply from 30° to 95° but not beyond, even though the " fastest 

 point" should be moved up to 80° or down to 40° ; beyoni' 

 these points a new law applies, and instead of squaring the dif- 

 ference of temperature and multiplying that quantity by the 

 coefiicient of temperature, this latter must be multiplied by thi 

 difference of temperature (always reckoned from the "fastest 

 point " of the chronometer under trial) raised to a power betweeni 



the square and the cube, ox x ^, for which good reasons 



be given. 



This being explained, it will be easy to perceive the use of til 



