December io, 1914] 



NATURE 



405 



diseases affecting tropical or subtropical plants, such 

 as the sugar-cane, banana, sweet-corn, etc., which are 

 of no economic importance in this country. If, how- 

 ever, the cultivation of tobacco is to have any great 

 development in Great Britain, a reference to these 

 pages is indispensable as a guide to the destructive 



Fig. I. — Tobacco-leaf from the hothouse, showing the typical red- 

 brown shrivelled spots ol the Granville tobacco wilt. The 

 remainder ot the leaf was green. Bacterium solanacearum 

 abundant in vascular system of the midrib and in many side 

 veins. Plant inoculated in stem, by needle-pricks, on September 

 23, 1905, using a pure culture of the North Carolina tobacco 

 organism. Pbotoi^rapbed February 20, 1906. 



attacks to which this crop is subject, and the condi- 

 tions which influence its successful growth. It seems 

 also to be substantially proved by the author's own 

 examinations and the weight of evidence which he has 

 been able to accumulate, that the various forms of 

 tobacco wilt, including those described by the Dutch 



Fig. 2. — Bacterium vazcularum in stem of sugar-cane 

 received in 1902 from New South Wales. The figure 

 represents a bundle in cross-section. The ground 

 tissue, endodermal sheath, and phloem are still free, 

 also a part of the xylem, including the two big pitted 

 vessels. Sectioned from paraffin and stained with 

 Flemniing's triple stain, the contrast being not exag- 

 gerated. 



and Japanese writers, are due to the same organism. 

 Bacterium solanacearum. Smith, which causes the 

 well-known rot of potatoes, tomatoes, and other 

 solanaceous plants. This parasitic disease of tobacco 

 has been known for the last twenty-five years in Japan, 

 and the damage caused is widespread in all countries 



NO. 2354, VOL. 94] 



where tobacco is cultivated; the loss has often been 

 enormous, and many planters have been driven to 

 harvest their crop while unripe and half-grown, in 

 order to save some portion of it. 



The specific communicable disease of the sugar-cane, 

 caused by a one-fiagellate schizomycete, B. vascularum, 

 Cobb, is, so far as is known, confined to this one host 

 plant. It is responsible for a considerable reduction 

 of sugar-content, and is apt to give trouble in the 

 sugar factory, gumming the machinery, and interfer- 

 ing with proper clarification and crystallisation. The 

 disease is most prevalent in the southern hemisphere, 

 and it is satisfactory to learn that it has not been 

 reported from the British West Indies or Porto Rico. 

 It is, however, specially liable to be transmitted in 

 cane cuttings, and planters in these islands are warned 

 to be careful to guard against its introduction. The 

 question of the origin and nature of the " gum," which 

 is such a tj'pical feature accompanying vascular bac- 

 terial diseases, is extremely interesting, and it 

 is disappointing to find that nothing has been done 

 on this point since Greig-Smith's work in 1904. His 

 researches, undertaken upon the lines of qualitative 

 chemistr}-, are entirely confirmatory of the bacterial 

 origin of the "gummosis," as he concludes from tests 

 of the chemical reactions that the " gum " and the 

 bacterial slime from pure cultures on agar are 

 identical. Apparently the mucilaginous substance 

 blocking up the vessels is a bacterial zooglea, but its 

 exact composition has not yet been determined, and 

 remains one of the many unsolved problems of bio- 

 chemistry. It would seem that these plant-gums are 

 derived by the bacteria from the saccharine contents 

 of the cell-sap, and are clearly not a degeneration 

 product of the cell-wall, as was formerly supposed. 



The book is profusely illustrated with excellent 

 photographs and drawings showing all stages of the 

 diseases cited and innumerable inoculation experi- 

 ments. M. C. P. 



ZOOLOGY AT THE BRITISH ASSOCIATIOW 



SECTION D held its meetings in the lecture 

 theatres of the Universities of Melbourne and 

 Sydney, and presented a full and varied series of 

 papers. It will be noticed from the subjoined sum- 

 mary that about one-half the time of the section was 

 devoted to the consideration of researches on Austra- 

 lian material. 



Recent Work in Antarctica. 



A discussion on the past and present relations of 

 Antarctica was arranged by Section D, in conjunction 

 with the Sections of Geology, Botany, and Geography. 

 An account of the contributions of the geologists and 

 geographers to this discussion appeared in N.ature 

 of October 19 (p. 241), so that it is only necessar)' to 

 refer here to the observations made by Mr. Hedley 

 and Prof. Seward on the biological relations of Ant- 

 arctica. 



Mr. C. Hedley stated that naturalists have deduced 

 the age, climate, contour, fauna, and flora of Tertiary 

 Antarctica from the nature of Antarctic refugees now 

 living in southern lands. For instance — (i) the mono- 

 tremes, once perhaps numerous, are represented by 

 two widely different types which survive in Australia, 

 Tasmania, and Papua ; the bones of other monotremes 

 occur in South American deposits : (2) the Thylacines 

 are recent in Tasmania, and fossil in South America 

 and Australia. Either we must consider that these 

 groups arose independently in each hemisphere, or 

 tha* they spread from the one to the other. In the 

 latter case a south f>olar land offered the most direct 



