Welwitschia

202 NATURE of the body capable of. communicating the highest temperature, but by thts, plus the mmor radiators or convections of the cooler bodies? words I have put in italics distinctly imply such an assumption. L: He seems to forget that I did, in the first place, observe and record the temperature of the surrounding medium. It was the 19° C. which served as my starting-point. As no additional radiations were introduced beyond those of the flames to be experimented upon, and the blackened bulb of my thermometer was surrounded by polished reflecting metal surfaces on sides, except that exposed to the flames, all the subsequent incretnents of heat were unquestionably due to the radiators from those flames, whether they came directly from the flames themselves or were received and reflected from the back and sides of the polished chamber. Fully admitting the desirability of a continuous record of the heat thus communicated to the surroundings of the thermometer during the experiments, I nevertheless firmly maintain that, rude as it was, my apparatus (I refer not to the thermometer, but to its adjuncts) was far superidr to Capt. Ericsson's. Mine was liable to a small source of error from a possible accidental irregularity of radiation by the thermometer bulb, but his was specially devised to ensure a large amount of such irregularity, continually increasing with the progress of the experiments. It is not a little surprising that so caref1tl and luxurious an experimentalist as Capt. Ericsson should have overlooked the fact, that the very precautions which he so elaborately introduced to secure equal radiation from his bulb are precisely adapted to produce the contrary result. The arrangements by which his thermometer is "enclosed in an exterior vessel charged with water kept at a constant temperatL:re " of 60° by .c?mmunication with a cistern, directly vwlate the condttwns demanded by the Newtoman law of radiation, ?f which Capt. Er:csson i? so able a champion ; for as the expenrncnt proceeds With an mcreasing number of flames, and consequent rising of the thermometer, this constant temperature of the water jacket goes on steadtly augmenting the difference between the temperature of the bulb and that of its surroundings, and consequently secures just what it is intended to prevent, v1z. a variable radiation. \Nhat is required to secure a constant the bulb is not the constant temperadegree of radiation ture of the surroundwgs, but a temperature steadily increasing at the same rate a' that of the bulb, in order that the dijfirential and not the temperatur": of the surrounding medium, &c., should remam consmnt. Th1s was rudely obtained in my simple apparatus, as both the thermometer and its surroundings were simultaneously influenced by the same radiations. Capt. Ericsson takes great pains to controvert my "assumption that the inten>ity of a gas flame is proportional to the gas consumed." This is unnecessary, inasmuch as I never made any such assumption, but have, on the contrary, endeaVJured to prove that such cannot possibly be the case, by showing what becomes of the radiations from the interior of a large solid flame. If he will read chaps. 7 and 8 of " The Fuel of the Sun," he will see how and why this has been done, and learn the true bearings of the experiments under discussion upon this W, MATTIEU \VILLIAMS subject. all P.S.-The present is a suitable opportunity for asking a question which doubtless the philological readers of NATURE can easily answer. Many writers use the words "diathermancy," "diathermanous," "athermanous," &c., rather than "diathermacy," diathermous," &c. Why is this? We do not s1y "rhermatzal" or "therma1lometer," &c. Why then should we depart from the analogy of ancient usage 'in con: structing the more modem compounds of the same root? Pollen-eaters . MR. HART's in vol. 161, is interesting to who have patd attentwn. to the subject of fertilisation by msect agency, and would be stlll more so if he could furnish the names of the species of both plants and Syrphidm that have come tinder his observation. May 1 take this opportunity of calling the attention of the readers of NATURE to a suggestion which I made some months since in the 'Journal of Botany, and which has at present met W.ith no response? I believe no greater service could be rendered to this department of physiological botany than a series of the species of insects which frequent and assist in the fertilisation of our wild flowers. I know of no such list even L.Tan. 16, 1873 with respect to our commonest flowers. Here is a wide field for observation during the next season. London, Jan. 7 ALFRED W. BENNETT P.S.-At the time of writing the above, I had not seen Dr. Buchanan White's article in the Jannary number of the "Journal of Botany," on "The Influe11.ce oflnsect-agency in the Distribution of Plants," an admirable introduction to the series of papers I had in my mind. Welwitschia IF you will kindly permit me, I wish to make an addition to your notice of my paper on" Welwitschia" read at the Linnean Society on the 19th ult. That paper was and put in Dr. Hooker's hands about three months arro · and the reading it was del:'yed until I had seen recently published memOir on Comferre and Gnetacere. After perusing that valuable 'York, I added a small appendix to my paper, and it is to the omtss!on of the remarks contained therein that I wish to direct attention. In the description of the male flower, Strasburger and I almost completely agree. It possesses two ouier parts of the perianth, two inner parts, six stamens, which I believe to arise by branching from two primordial stamens, although Strasburger does not agree with me in this, and two c.arpels. The formula of the flower may be expressed thus : Ca2 Co 2 An 2 3 Gn 2 In female flower I had very great difficulty in coming to a concluswn as to the value of the two outer parts, but :he inner I concluded was a covering of the nucleus, an ovular integument, and not carpellary.. only two ways of deciding what was the Significance of the two outer parts, either by wlth the male flower, or by comparing them with the parts m the flowc;rs of Ephedra and Gnetum. I applied to Dr. I_looker for specimens of these genera, and he has kindly promtsed them for me. As Strasburger's material for exa_mmatwn of Ephedra and Gnetum was imperfect, it is sttll of Importance to examine both in detail. Beina therefore (the study obliged to fall back on comparison with the male of development alone not being sufficient for the purpose), I descnbed the two parts as forming a perianth, although I could not feel certam that I was ::orrect in so doing aad could not explain the occurrence of the short stalk unde; them no such stalk existing in the male. On looking at Strasburger's figures of Ephedra, I at once saw that I had been in error in the outer parts as forming a perianth, and in the appendtx stated that they were carpellary. The formula would therefore be (...truncated)