July II, 1878] 



NATURE 



279 



is simply a convenient way of expressing it in one line j and it 

 is not printed as he has misquoted it above. 



George Henslow 

 6, Tichfield Terrace, Regent's Park, N,W. 



[I am obliged to my friend Mr. Henslow for correcting 

 my oversight in not accurately noting the form of his formula. 

 The fact, however, that the sentence is, as, Mr. Henslow admits, 

 put in a form which is adapted for ' ' mathematical students 

 only," in a work intended for beginners, seems to furnish a 

 strong justification of the main point of my criticism. — 

 A. W. B.] 



Alumina 



It may interest your readers to know that pure alumina 

 dissolved nearly to saturation before the blowpipe in an acid 

 flux, such as a bead of phosphoric acid, invariably causes that to 

 assume a pale but beautiful sky blue on cooling. 



In an alkaline flux such as a bead of boric acid containing 

 sufficient soda to dissolve it to saturation, alumina causes the 

 bead to assume a pale red colour on cooling. 



The greatest care has been taken to ascertain that the 

 materials are absolutely free from any metallic or other oxide 

 which might produce such colours, and the resulting beads have 

 been shown to several gentlemen, as Messrs. Hunt and Roskell, 

 Mr. Hutchings of Freiberg, and others. 



Might not these facts then afford us some clue (so much 

 wanted) to the cause of coloration in the sapphire and ruby ? 



London, July i W. A. Ross 



A Subject-Index to Scientific Periodical Literature 



I HAVE been occupied for years in drawing up a classified 

 index, not only to the titles of papers, but to what is still more 

 wanted, to the facts contained in those papers. As yet I have 

 met with scant encouragement. A. Ramsay 



Kilmorey Lodge, 6, Kent Gardens, Ealing, W., July 8 



CLUB-ROOT 



ALL our readers who are agriculturists or practical 

 gardeners will be familiar with the disease called 

 in England "Club-root," or "Finger and Toes," or 

 "Clubbing." It seems almost to confine its ravages to 

 cruciferous plants, and often causes great destruction to 

 large crops of turnips, cabbages, cauliflowers, not to 

 mention what disappointments it may occasion to the 

 growers of wallflowers, Brompton stocks, candytufts, and 

 many other favourite flowers belonging to this large 

 natural family. Not only is it well known, but it has 

 often been Avritten about, as the pages of our contem- 

 porary, the Gardeners' Chronicle, and most works on the 

 cultivation of gardens, will abundantly prove. 



The question of what did it consist of was often asked, 

 and the answer was that it was caused by some insect or 

 another, and some poor beetles and flies were signalled 

 out as those which laid their eggs in the tissues of the 

 young roots of the plants attacked, and, if we are not 

 mistaken, this is the general belief to this present 

 moment. The explanation never was, however, satis- 

 factory. True, in the advanced stage of this disease 

 insect larvae were to be found in the club-like swellings 

 of the roots ; but in the very early stages no trace of 

 larva or t^g of any insect was to be seen, and yet the 

 club-root disease was clearly there. 



In the Botaniscke Zeitung for May 14, 1875, there 

 appeared a short abstract of a paper read by M. 

 Woronin, before the Botanical Section of the Natural 

 History Society of St. Petersburg, on the Sth of March 

 of the previous year, on the cause of this disease, and 

 within the last few weeks we have received the full 

 memoir, illustrated with upwards of fifty figures. This 

 memoir is in Russian, but, thanks to a colleague (Prof. 

 R. Atkinson), the writer has been able to glean a notion 

 of its most interesting contents, in which he has been 

 much assisted by the beautiful figures. The disease is 



known in Russia as " Kapustnaja Kila " (Kapusta = 

 Cabbage, Kila = Hernia). About three years since it 

 was so extremely prevalent that the vegetable crops about 

 St. Petersburg failed, and the government ordered an in- 

 vestigation, from which much information was obtained as 

 to the means adopted in different countries for its cure : 

 such as sowing the ground, before planting the crop, 

 with common salt, wood ashes, or, before all, soot. Every 

 one knows, too, that in transplanting the young crucifers 

 into their permanent beds that it is customary to pinch 

 off the swollen portions, and then, if favourable weather 

 followed, the newly-formed roots could well keep ahead 

 of any fresh appearance of the disease. But M. Woronin 

 went scientifically to work, and he was not long in dis- 

 covering that the cause of the disease was a parasitic 

 vegetable which seemed to have some affinities with the 

 Myxomycetes on the one hand, and the Chytridiaceas on 

 the other, and the result of constant researches carried on 

 through 1875, 1876, and last year, have resulted in nearly 

 the whole life-history of this new plant being discovered. 

 It is called Plasmidiophora brassicce, and is decidedly 

 very nearly allied to the Chytridia, but the new forms of 

 this group daily coming to light, appear so different in 

 their development, that much more must be known about 

 them ere any satisfactory classification can be attempted. 

 One most striking feature in the new plant is indicated 

 by its generic name ; this will be best understood by a 

 short history of the plant's life. Take an old well-developed 

 knob off a club-root, and examine the tissue ; most of the 

 parenchymatous cells will be found enlarged, their starchy 

 contents gone, and they themselves gorged with a mass 

 of spore-like bodies ; by the ordinary disintegration of the 

 cellular tissue these spores will get released, and after a 

 lapse of six days, out of each spore will proceed the whole 

 of the contents, which, colourless, but nucleated, will 

 move about like so many minute amoeba ; these Plas- 

 modia will then attach themselves to the delicate root- 

 hairs of the nearest young cruciferous seedling. One end 

 of the Plasmodium is attenuated like a cilium. The spores 

 soon penetrate into the cells, where they will look just like 

 Myxamoebae. Filling the cells up with delicate plasmodic 

 projections, they will next soon develop lots of spores, 

 which will further contaminate the cellular tissue of the 

 root, and in process of time the formation of the clubbing 

 will be seen. 



Sometimes the ripe spores are spherical, sometimes 

 they are twin-like, or lenticular. If cabbage or turnip 

 seeds be sown in a watch-glass and supplied with dis- 

 tilled water, and shortly after the first appearance of 

 germination, a number of spores of Plasmidiophora 

 brassicce be added to the water, these will be found to at 

 first float freely in the water, but sooner or later will sink 

 and attach themselves to the delicate root-hairs of the 

 little seedlings, and in this way their whole history, so far 

 as now known, may with facility be traced. It seems 

 noteworthy that the whole mass breaks into spores all at 

 once, as in Chytridium proper. There would seem to be 

 as yet no conjugation detected, and the Plasmodia would 

 appear as if they absolutely engulfed the starch granules 

 on which they feed. 



It must be a matter of regret that this memoir is written 

 in a language known unfortunately to so few scientific 

 botanists. If the learned author knew only Russian it 

 would be absurd and unreasonable to record this regret, 

 but to one knowing French and German, as M. Woronin 

 does, it would have been no trouble to hare increased a 

 hundredfold the grateful readers of this important memoir. 



E. Perceval Wright 



SCIENCE IN SCHOOLS 



THE following article on Sir John Lubbock's Bill on 

 the introduction of science in elementary schools 

 appears in Monday's Times : — 



