NATURE 



\Nov. 2, 1 871 



having seen any original or detailed account of the phenomena 

 to which Mr. Webb allude;, I am unable to say whether they 

 fulfil these theoretical conditions, but I believe that something 

 more may be learned by means of careful observations specially 

 directed to the elucidation of the questions I have suggested. 

 W. Mattieu Williams 

 Woodside, Croydon, Oct. 23 



Pendulum Autographs 



It may interest some of your readers to know that they can 

 for themselves observe in the most accurate manner the motion 

 of the compound pendulum described by Mr H. Airy* by merely 

 attaching the ends of a fine thread to two points in the ceiling of 

 a room, and suspending a leaden bullet by means of a second 

 thread tied to the middle point of the former, so that the bullet 

 may just escape the lloor. Lay underneath a large sheet of white 

 paper ruled with two dark lines at right angles to each other to 

 correspond to the two axes of vibration. It is Mr. Airy's expe- 

 riment with the hoop on an extended scale. The motion of the 

 bullet, unimpeded by contact of pencil with paper, is graceful 

 and accurate in the extreme. 



Perhaps the most remarkable case is that in which the two 

 points of suspension are taken about an inch apart, and the third 

 about half an inch below them ; the pendulum will now keep 

 reversing its motion as uniformly as before, and apparently with- 

 out any adequate cause, a matter of astonishment to the unin- 

 itiated spectator. 



I believe the general equation to the path, including all the curves 



described, will be found to be \ln cos~'^ ' - = ^J m cos^'^ _ , 



where the particle starts from the point [a, b) and is attracted to 

 the axes of X and I ' by forces = - >iy and - nix respectively. 

 Woolwich, Oct. 24 Geo. S. Carr 



Exogenous Structures in Coal Plants 



I CORDIALLY agree with your recommendation that discussion 

 on the Exogenous Stems of the Coal Measures should cease for the 

 present. It is evident that I shall not convince my two opponents, 

 and they are as far as ever they were from convincing me. But I 

 must request that in justice to me, you will allow me to enter a 

 protest against the last paragraph of Prof. Dyer's article, in 

 which he objects to my applying the term Protoplasmic to the 

 cambium layer, and endeavours to show that I am two hundred 

 years behind the age in my physiology. I cannot but think that 

 Prof. Dyer, when he penned that paragraph, knew perfectly well 

 in what sense I u'sed that expression. I meant by it nothing 

 more than is implied in the following sentence, taken from Prof. 

 Balfour's " Manual of Botany," p. 43, which certainly does not 

 belong to the age of Grew : — 



" External to the woody layers, and between them and the 

 bark, there is a layer of mucilaginous semifluid matter, which 

 is particularly copious in spring, and to which the name Cam- 

 bium has been given. In this are afterwards found cells, called 

 Cambium Cells, of a delicate texture, in which the protoplasm 

 and primary utricle are conspicuous." 



W. C. Williamson 



Fallowfield, Oct. 25 



*^* This correspondence must now close. — En. 



Classification of Fruits 



It seems from the numerous attempts that have been made 

 that a philosophical classification of fruits is either unattainable 

 or practically of very little value when attained. At any rate 

 working botanists have, as a rule, discarded the majority of the 

 carpological terms that are to be found in text-books as too cum- 

 brous or too uncertain in their application. Among the I.itest 

 attempts at simplification in the matter of the classification of 

 fruits are those of my friends Prof. Dickson and Dr. M'Nab (see 

 Nature, vol. iv. p. 475). Both of these areopentosome ciiiicism 

 on matters of detail, but I can hardly expect you to accord me space 

 to point out what I believe to be the merits or shortcomings 

 of their respective schemes. I should also trespass loo much on 

 your courtesy and on the patience of your readers did I enter into 

 any engthened explanation of the following scheme, in which I 

 have adopted to some extent the nomenclature of Prof. Dickson 



* Sec Nature, vol. iv pp. 310, 317. 



and Dr. M'Nab, and which I offer for consideration solely on the 

 grounds of e.'^pediency and simplicity: — 



Classification of Monothalaniic Fruits 



A. Ripe pericarp uniform 



Fruits indehiscent I. Nuts or Achrenocarps. 



Fruits dehiscent II. Pods or Regmacarps. 



B. Ripe pericarp of two or more layers of different substance ' 



Seeds within a hardened ) ttt ci r ■. t> I 



, III. Stone-fruits or Pyrenocarps. i 



endocarp I I 



Seeds embedded in pulp* IV. Berries or Sarcocarps. | 



I. Nuts or AcIuTHOcarps \ 



WlNCLESS — ' 



Fruit of one carpel, or, if of more, apo- 

 carpous Achene 



Fruit of more than one carpel 



Carpels ultimately separate but inde- 

 hiscent Carcerule 



(Cremocarp). 

 Carpels inseparate 

 Pericarp adherent to the seed . .- Caryopsis. 

 Pericarp free from the seed, within a 



cupule Glans. 



Winged Samara 



II. Pods or Regmacarps 

 Fruit of one carpel 



Opening by one suture Follicle 



two sutures Legume 



transversely Loraentum 



(Dichisma,7IA^>/') 

 Fruit of more than one carpel 



Opening by pores or sutures . . . Capsule 



(Siliqua) 

 (Regma) 

 (Conceptaculum) 

 (Tryma, &c.). 

 Opening transversely Pyxis. 



III. Stone-fruits or Pyrenocarps 

 Carpels one or more, superior .... Drupe 



(Fibro-drupeasin 

 Cocos, Grai'ia, 

 sp., &c.). 

 Carpels one or more, adherent to, or ) p 

 enclosed within a fleshy receptacle . . j 



(Sphalerocarpium, 

 asin Hifpophae) 



W. Berries or Sarcocarps 



Seeds embedded in pulp Bacca 



(Hesperidium) 



(Uva) 



(Pepo). 



I believe that the foregoing arrangement will include most 

 of the varieties of fruits and seed-vessels, though, as in all similar 

 cases, exceptional forms are not readily s >rted into their proper 

 place ; the fruit of such Cassias as C. Fistula, generally called a 

 lomentum, is a case in point. For general purposes the varieties 

 enclosed in brackets may well be omitted, save in the case of so 

 well known and constantly used a term as siliqua, which, despite 

 Prof Dickson's veto, I think is too useful praciically to be lightly 

 abandoned. MAXWELL T. Masteks 



The Berthon Dynamometer 

 Absence from home, and many engagements, have prevented 

 an earlier reply to " W. R.'s" letter in Nature, October 5. In 

 my previous communication I believe I gave the address of the 

 inventor, to whom I thought reference might naturally be made ; 

 in order, however, to meet " W. R.'s" wish, I will explain the 

 construction of the very simple but efficient instrument in ques- 

 tion. It is merely a V gauge, formed of two pieces of thin brass 

 converging at a very acuce angle, and graduated along one of the 

 edges ; the divisions being viewed through a lens held in the 



* The pericarp i'^ here understood as including not only the ripened c.^^- 

 pcUary wall, V^ut .-ilso any adjunct to it which in process of development may 

 he combined with it. In the same manner the pulp may be a production 

 from the carpel or from the seed itself 



