September 20, 1900] 



NA TURE 



495 



•especially as many of the species enumerated are simply 

 saprophytic forms, whose presence can do no injury. 

 The enumeration of such species is, from a scientific 

 standpoint, of great value ; but they are altogether out 

 of place in a work which should place before practical 

 men the outcome of scientific research in language 

 •divested of scientific technicalities. The author con- 

 siders it essential that each fungus should possess a 

 popular name in addition to its scientific one, and there 

 is some justification for this idea, especially when 

 such names are of local origin, and express a 

 •definite idea, as "collar-rot," " wither-top," &c., 

 but it is more than doubtful whether the English render- 

 ing of the scientific name, as " West Australian Septoria," 

 ■or " Gloeosporium-like Colletotrichum," will be adopted 

 by the fruit grower. Fifty-one species of fungi found on 

 citrus trees are described as new to science ; this is a 

 somewhat daring piece of work in the comparative 

 absence of literature and herbaria. It must be borne m 

 mind that the fact of a fungus not agreeing with any 

 species recorded in Saccardo's " Sylloge Fungorum " by 

 no means justifies an author in describing it as new to 

 science. 



In defining parasites and saprophytes respectively, the 

 author states that it is not always easy to decide between 

 the two, and the crucial test, by means of pure cultures, 

 is not alluded to. This, however, may not be due to lack 

 ■of knowledge or desire on the part of the author, who, as 

 vegetable pathologist, is probably expected to cover too 

 much ground ; hence fundamentals, which consume time, 

 iire apt to be neglected in favour of less exact methods, 

 which may meet with approval for the time being. 



The twelve coloured plates illustrating the most pro- 

 nounced and destructive forms of disease attacking lemons 

 and oranges are excellent in every respect, and should 

 prove of great service in enabling planters to recognise 

 at an early stage the appearance of a disease which, if 

 neglected, might prove disastrous. The most approved 

 methods of treating the various diseases are given in 

 tabular form. 



Missouri Botanical Garden. Eleventh Annual Report. 



Pp. 144 ; 58 plates. (St. Louis, Missouri, 1900.) 

 This volume is almost entirely made up of four scientific 

 papers representing work carried out in connection with 

 the Missouri Botanical Garden. The papers are : a 

 dxstnsG oi Tascodiuin distichum known as " peckiness," 

 also a similar disease of Libocedrus decurrens known as 

 pin-rot, by Dr. H. von Schrenk ; Agaves flowering in the 

 Washington Botanic Garden in 1898, by Mr. J. N. Rose ; 

 A Revision of the American species of Euphorbia of the 

 section Tithymalus occurring north of Mexico, by Mr. 

 J. B. S, Norton ; and a Revision of the species of Lo- 

 photocarpus of the United States, and a description of a 

 new species of Sagittaria, by Mr. J. G. Smith. Dr. von 

 Schrenk's paper has already been noticed (vol. Ixi. 

 p. 452). 



Mr. Trelease, the director of the Garden, shows by 

 these papers and his report that valuable work is being 

 ■done. A small synoptical collection representative of 

 the principal natural orders of flowering plants has been 

 installed in the central part of the Garden, where it is 

 proposed to continue it as a convenient means of enabling 

 teachers in elementary schools to demonstrate to their 

 pupils the characters of the larger plant groups. The 

 total number of species and varieties now cultivated in 

 the Garden is nearly ten thousand. 



Mr. Trelease devoted a couple of months last summer 

 to the study of the botany of the Alaskan coast region 

 and the islands of Bering Sea, as a member of the 

 Harriman Alaska Expedition. The scientific results of 

 his work will, no doubt, be published after the large 

 amount of material collected has been subjected to critical 

 study. 



NO. 161 2, VOL. 62] 



LETTERS TO THE EDITOR. 

 \The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond -with the writers of rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.'^ 



Atmospheric Electricity and Dew-ponds. 



It is not my intention to enter into controversy with such 

 autl>orities as Mr. Aitken or Mr. Wilson. I wish only to de- 

 scribe certain phenomena which have come under my notice, in 

 the hope that I may help to throw some light on a subject of 

 great importance, theoretical as well as practical. 



On the chalk hills in the south-east of England there are a num- 

 ber of ponds known as dew-ponds. One of these was described 

 by Gilbert White (" Natural History of Selborne," Letter 29). 

 There is a pond of considerable size at one of the highest points of 

 the main ridge of the South Downs close to Chanctonbury 

 Ring. From its position it is obvious that this pond can only 

 be fed by water precipitated into it directly from the air. Yet 

 it always contains a considerable volume of water. At the end 

 of the dry weather last year, when most of the ponds in the 

 valleys were empty, this dew-pond still contained several thou- 

 sand gallons. How does this pond obtain the enormous 

 quantities of water necessary to compensate for the rapid 

 evaporation in such an exposed position, and also to supply 

 large flocks of sheep ? 



It appeared to me that therejwas but one possible explanation : 

 a diff"erence of electrical potential must cause an attraction 

 between the particles of moisture and the summit of the hill 

 upon which the pond is situated. It is, of course, well known 

 that drops of rain, &c., usually have an electrical charge, but it 

 was necessary to ascertain whether this was capable of producing 

 such a great effect In order to test this point I took two 

 porcelain basins of equal size and suspended them by means of 

 silk threads from stakes driven into the ground at a high part of 

 the ridge of the South Downs. In each of these basins was fixed 

 an upright piece of sheet-copper. The two pieces of apparatus 

 were placed in exactly similar positions and were in every respect 

 identical, except that in the one case the copper screen was con- 

 nected to earth by means of a wire, whereas in the other case it 

 was insulated by the silk threads. 



The apparatus was left thus during the night of April I, 1899. 

 There was a thick mist on the hills, so much so that I was 

 unable to select the most favourable position for the apparatus. 

 In the morning the amount of water in the two basins was 

 measured. In the basin with the insulated screen there were 

 15*5 c.c. of water; in that with the screen connected to earth 

 there were l8'0 c.c. This clearly confirmed my theory, for the 

 insulated apparatus would tend to acquire an electrical charge 

 from the particles of moisture. Consequently the attraction 

 would be less than in the case of the apparatus which was not 

 insulated. The insulation must have been very imperfect, for the 

 silk became saturated with moisture as soon as the apparatus was 

 erected. The position chosen, also, was not so favourable as 

 it might have been. Nevertheless there was a difference of 

 16 per cent, in the quantities of moisture collected. 



I intended to repeat and extend the experiment, but I have 

 been unable to find an opportunity. I hope that this letter 

 will call attention to a matter of considerable interest. 



Arthur Marshall. 



Chemical Department, Woolwich Arsenal, September 10. 



Huxley and his Work. 



Mr. Henkel's quotation from " One Hundred and One 

 Great Writers " (Nature, September 6) reminds one that the 

 taunt of being a populariser was familiar enough to Huxley 

 himself. It recalls also the little side-thrusts with which in 

 return the detractors were sometimes honoured. In the preface 

 to vol. viii. of the " Collected Essays," for instance, Huxley 

 remarks : — 



" The popularisation of science has its drawbacks. Success 

 in this department has its perils for those who succeed. The 

 people who fail take their revenge, as we have recently' had 

 occasion to observe, by ignoring all the rest of a man's work 

 and glibly labelling him a mere populariser. " 



