458 



KNOWLEDGE & SCIENTIFIC NEWS. 



[JlINIi, 1906. 



white screen inside a room faciiij; the point of sunrise. 

 The bands were easily seen, and were g^enerally straij^ht, 

 parallel, and not at all likely to be confounded with the 

 irrof^ular shadows produced by convection currents near the 

 screen. .\s the result of 75 obs( rvations, he makes the 

 following conclusions : — 

 (a) The orientation of the dark bands, on a screen of per- 

 pendicular rays, is constantly parallel to the part of 

 the mountain edfje over which the sun is rising or 

 setting. 

 {h) The direction of their displacement is always per- 

 pendicular to their orientation, but may be in one of 

 two directions direct or retrograde, 

 (c) The velocity of the motion of the bands varies con- 

 siderably from time to time, which may have some 

 relation to the force of the wind, as the most rapid 

 movements occur during high winds, and the slow ones 

 during calm weather. 

 ((/) The bands cease to be visible two or three seconds 

 before the sun sets, and may become visible several 

 seconds after sunrise. If the disappearance of the sun 

 takes place behind a vertical screen, the time of appari- 

 tion may be lengthened to 12-15 seconds, 

 (p) .At first the bands are wide and far apart, becoming 

 sharper and straighter later. Their width usually was 

 3-4 cm., and distance apart 3-4 cm., but might vary 

 from 1-20 cm. The width and distance apart appeared 

 to vary with the velocity of translation. 

 {/■) The colour of the bands was gencrallv of a uniform 



grey. 

 The distances of the mountains over which the phenomena 

 have been observed, have varied from 6-36 km., with eleva- 

 tions of 30-22"'. In spite of these variations, the features 

 of the bands have been fairly constant. — Comjifes Ucndus, 

 15, 1906. 



Vesuviarv Origin of Paris Fog, April 11th, 

 1906. 



In corroboration of the evidence furnished by the many 

 striking sunsets during the latter part of .\pril, there may 

 be considered the finding of volcanic dust in Paris just 

 after the eruption. M. S. Meunier describes how, during 

 the dry, yellow fog which enveloped Paris on the nth of 

 -April last, he exposed gelatinised plates near the Ouay 

 Voltaire, and after treating these with water, he obtained 

 a deposit from which the soot and organic matter were 

 removed by Thoulet's heavy liquid. There remained an 

 extremely fine residue, the microscopic examination 

 of which showed almost perfect identity with a sample of 

 the dust emitted from Vesuvius in 1822. The chief differ- 

 eiice consisted in the presence with the Paris dust, of small, 

 perfectly spherical globules of oxide of iron. It thus ap- 

 pears most probable that the Paris fog was produced by a 

 fine rain of cinders which had been carried from the 

 \'esuvian area. 



Photography of Corona without Eclipses. 



MM. .\lillochau and Stephanik propose to start a now 

 attack on the problem of photographing the solar corona 

 during daylight, by combining the use of the spectrohelio- 

 graph and coloured scre'ens. As the corona is projected on 

 a background of extremely bright sky, it is hoped that the 

 relative intensity of the corona will be enhanced if a screen 

 is interposed which cuts off all light except that of a green 

 colour in the region of wavelength 5303. Then, by setting 

 the secondary slit of their spectroheliograph on this line, 

 the increased contrast produced may render possible the 

 record of the coronal form. Preliminary attempts at 

 Meudon are said to have given encouraging results, and 

 the apparatus is to be transferred to the Observ.atory on 

 the summit of Mont Blanc, where the absence of the lower 

 and denser layers of the earth's atmosphere may further 

 conduce to success. 



BOTANICAL. 



By G. Masses. 

 Sexuality in the Mucorineae 



It has long been known that a sexual mode of reproduc- 

 tion existed in the group of fungi known as the Mucor- 



inea;, of w'hich the moulds common on bread and various 

 fatty matters are well-known examples. The result of 

 sexual fertilisation consists of a structure called zygospore, 

 which, after a period of rest, germinates, and at once gives 

 origin to a mucor-plant. A second form of reproduction 

 produced asexually is much more general than the sexual 

 condition, and ajjpears under the form of myriads of minia- 

 ture pins, with golden heads, which eventually become 

 black. 



The subject of sexuality has recently been prosecuted from 

 a new standpoint, by Blakcslee. It was observed that some 

 .species could be readily induced to form zygospores, by 

 sowing spores obtained from a single fruit of the asexual 

 form. On the other hand, in many species, zygospores were 

 never produced from s|)ores contained in a single asexual 

 fruit, but only when a mass of spores from a zygosporic 

 culture was used. When isolated cultures of the last- 

 named group were grown in proximity on a suitable 

 medium, it was observed that zygospores were formed along 

 the line w'here the mycelium of the two colonies met. This 

 suggested the idea that such species consisted of strains, 

 or races, which, when grown apart, produced only a sexual 

 fruit or sporangia, but which produce se.xual fruit, or zygo- 

 spores, when the two physiologically different strains are 

 grown in contact. These are designated respectiv'ely -f- 

 and {-) strains, which is considered as non-committal as 

 to the sexual relation of the respective strains. 



This condition of things is essentially similar to that 

 present in dioecious plants and animals, although morpho- 

 logical differentiation is not obvious in the Mucorineae. 



The term heterothallic is used to designate those forms 

 that are dioecious, and homothallic is applied to the her- 

 maphrodite species. Hybrids have been produced from (-f-) 

 and (-•) strains of different species of the heterothallic type. 



The following is a part of the author's summary of this 

 important discovery : — 



" The production of zygospores in the Mucorineae is con- 

 ditioned primarily by the inherent nature of the individual 

 species, and only .secondarily by external factors. 



" According to their method of zygospore formation, the 

 Mucorinese may be divided into two main groups, which 

 have been termed respectively homothallic and hetero- 

 thallic. 



" In the homothallic group, comprising the minority of 

 species, zygospores are developed from branches of the same 

 thallus or mycelium, and can be obtained from the sowing 

 of a single spore. 



" In the heterothallic group, comprising probably a large 

 majoritv of the species, zygospores are developed from 

 branches which necessarily belong to thalli or mycelia, 

 diverse in character, and can never be obtained from the 

 sovving of a single spore. Every heterothallic species is, 

 therefore, an aggregate of tw-o distinct strains, through 

 the interaction of which zygospore production is brought 

 about. 



" These sexual strains in an individual species show in 

 general a more or less differentiation in vegetative luxuri- 

 ance, and the more or less luxuriant may be appropriately 

 designated by the use of ( + ) and ( - ) signs respectively. 



" A process of imperfect hybridisation will occur between 

 unlike strains of different heterothallic species in the same, 

 or even in different genera. 



" From the foregoing, it may be concluded that the 

 formation of zygospores is a sexual process ; that the 

 mycelium of homothallic species is bisexual ; while the 

 mvcelium of heterothallic species is unisexual ; and finally, 

 that the (-f ) and ( - ) strains of the heterothallic group repre- 

 sent the two sexes." 



The zvgospores require a period of rest before they are 

 capable of germination. 



Marine F\ingi. 



H. E. Petersen has studied the microscopic fungi be- 

 longing to the Chytridine.x', parasitic on marine algae. 

 Twentv-five species were collected on the Danish coast, and 

 further north, and are described in detail in Overs, k. JDansJce. 



rivrnsi: Schh. FnU;. 



New British Algae. 



Notwithstanding the work of centuries in investigating 

 the flora of Britain, additional new, or previously' unre- 

 corded, species continue to be found. Batters, in Jmirnal 



