May 1, 1899.] 



KNOWLEDGE. 



117 



In Stemonitis, on the contrary, the plasmodium gathers 

 itself together in a himp or mass, and first shows signs of 

 dividing up by the appearance of papillae on the surface ; 

 then at points corresponding with the papillse, dark-coloured 

 stems grow upwards in the gelatinous mass. Around 

 these stems, portions of the adjoining protoplasm gather, 

 and separate vertically from their neighbouring parts ; and 

 again, before maturity, the lower portion of the protoplasm 

 around each column moves upwards, leaving only the 

 delicate stalk which supports the arborescent sporangium. 

 Fig. 10 will explain these steps in development. 



It would seem as if the sporangium forms were the most 

 highly developed, and the plasmodiocarp form the more 

 rudimentary. We suppose that in the matter of advantage 

 to the organism there must be something to be said for 

 and against each form, for the plasmodiocarp must expend 

 less material on perishable walls and stalks, and, on the 

 other hand, be less open to the atmospheric influences ; 

 whereas the opposite in each respect must apply to 

 sporangia. If one of these forms be better than the other, 

 why does it not universally prevail ? and why do some 

 individuals of some species halt between the two opinions ? 

 We certainly do not know. This is one of the many cases 

 in which it is at least very difficult to see any advantage 

 gained by the variations of development of an organism. 



Sporangium Walls. — The walls of the sporangium vary 

 very greatly ; sometimes they consist of a single membrane ; 

 sometimes of two or even three membranes ; sometimes 

 they continue till by rupture they let loose the spores ; in 

 other cases, the whole, or the upper part only, early falls 

 away and discloses the system of hairs and the spores 

 within ; sometimes, as we shall see, they are furnished 

 with lime, at other times they are without it. 



In Cribrariii (Fig. 5) we have a very beautiful form of 

 sporangium, the wall of the lower half persists and forms 

 a cup, whilst the upper half in its mature state consists of 

 a network only of slender threads more or less thickened 

 at the points where they cross one another. 



In Dictydium we have again another very beautiful form 

 of sporangium — it consists of rays of longitude gathered 

 together at the pedicel and at the top as their two poles, 

 with much slighter transverse lines of latitude. The inter- 

 vening membrane falls away in whole or in part, and 

 leaves for the sporangium a basket of most delicate net- 

 work {see Fig. 11). 



Fig. 11. — Dictt/dium umhilicatum. Empty Sporangia. 

 X about 40 diameters. 



In some cases the exterior of the sporangium has a most 

 delicate surface, shining with iridescent colours. The 

 Lamprodcniia is a genus with several species distinguished 

 by this beautiful peculiarity. Our English species are 

 very attractive, but they are excelled in brilliance by some 

 tropical kinds. Of other genera, the Physarum psittacinum 

 is another species with iridescent sporangia, and derives its 

 name from its supposed resemblance to the colours of a 

 parrot. 



NOTES ON COMETS AND METEORS. 



By W. F. Denning, f.r.a.s. 



Swift'.s Comet (1899a). — This comet promises to be .an in- 

 teresting object for the telescope during May. Its approximate 

 positions will be as follow : — • 



R,A. Distance from 



1399. li. m. Dec. Briglituess. Sim. 



May 1 9+ 22" 33' 1-8 35° 



„ 5 23 50 + 27° 19' 1-7 44° 



„ U 23 26 -f 33° 13' 1-7 53° 



„ 16 22 53 + 40° 28' 17 63° 



„ 21 21 58 -f 48° 45' 1-8 75° 



„ 26 20 27 + 55" 48' 1-7 87° 



„ 31 18 22 + 56° 56' 1-5 98° 



June 5 16 40 + 51° 10' 1-2 106° 



„ 10 15 39 + 43° 2' 0-8 112° 



On May 1st the comet will be nearly twice as bright as when 

 discovered, so that it ought to be well visible to the naked eye. 

 It will rise about three hours before the Sun, and will be placed 

 six degrees S.S.E. from a Andromeda;. Moving rapidly to 

 N.W., it will pass one and a-lialf degrees S. of o Andromeda on 

 May l(!th, and on June 1st may be seen in the head of Draco, 

 close to 0. On June 16th the comet will be much fainter and 

 a few degrees west of J Herculis. Between about the middle 

 of May and June 12th, it will be visible all night, as it will be 

 placed within the circle of jierpetual apparition. 



Tuttle's Comet. — This comet may possibly be observed after 

 sunset in the N.W. region of Orion, but the strong twilight will 

 render it extremely faint. 



Holmes's Comet (1892 III.) is now gradually approaching 

 the e.arth, but its position in May will be such that it can only 

 be observed a short time before sunrise. In later months it will 

 be presented under more favourable conditions, as it is moving 

 northwards. The re-discovery of this singular comet is awaited 

 with special interest. 



Tempel's Comet (1873 II.) is also expected, and will be 

 favourably situated in the morning sky during ensuing months. 

 On May 1st its position will be in R.A. 281°, Dec. 5° south, and 

 close to the star 6 Aquila; (magnitude 4^i). The comet is 

 travelling slowly to the east, and its brightness increasing. 



Fireballs of March 1st. — In our notes for last month some 

 details were given of two fireballs recorded at 7h. Im. and 

 8h. 50m. on this date. The path of the former, as observed by 

 Mr. Astbury at Wallingford, Berks, was from 840° + 63° to 

 323° + 44°, which it traversed in two-and a-half seconds, and 

 the brilliancy of the object near the close of its visible career 

 greatly exceeded that of .Sirius. The meteor was seen by Sir 

 W. J. Herschel, at Littlemore, near Oxford, and he describes it 

 as the most brilliant which he had ever observed. The apparent 

 path was from about seven degrees preceding ji Cassiopeia^, and 

 descending almost vertically to witliin ten degrees of the 

 horizon. Duration two-and-a-half seconds. Light about four 

 times that of Venus. The same object was noticed by the Rev. 

 A. T. Fryer, of Cardiff, while walking between Bridgend and 

 Tondu,and his observation is described in the CantJir/iin Natural 

 Observer for March, 1899. He says the meteor descended in a 

 curve, roughly parallel with and to the north of the tail of Ursa 

 Major. The colour was very remarkable — very light blue on 

 the body but ending in brilliant red of a deep tone, like the red 

 which the winter sun shows in setting. The meteor was fish 

 shape. 



From the above observations I have endeavoured to compute 

 the real path. The meteor was a fine Geminid, and evidently 

 belonged to the same system as that which sujiplied the fireball 

 at about 8h. 50m. on the same night. The former was probably 

 first seen when at a height of seventy miles over Stourbridge, 

 and disappeared over a point five miles S.S. W. from Shrewsbury 

 at a height of twenty-five miles. Its length of path was about 

 fifty-five miles, and velocity twenty-two miles per second. This 

 differs materially from the ten miles per second found for the 

 fireball seen at a later hour, and it is probable that a mean of 

 the two values — about sixteen miles per second — would more 

 correctly represent the actual motion. The two fireballs are in- 

 teresting as proving that the Geminid radiant continues active 

 until the beginning of March. 



