October, 1910. 



KNOWLEDGE. 



411 



that the sugars travel in the bundle-sheaths of the leaf \eins : 

 but Czapek suggested that while diffusion goes on in all 

 living parenchyma cells, yet from rapid translocation over 

 long distances the sieve-tubes furnish the sole paths for the 

 products of assimilation as a whole. Czapek and Schimper 

 used Fehling's solution as a test for reducing sugars, but this 

 method is open to objections — the reagent is reduced by 

 organic substances other than sugars present in the plant, a 

 good deal of diffusion of cell-contents goes on in the hot 

 solution, and the small grains of copper oxide precipitated are 

 not always easy to observe. A much better sugar test — the 

 precipitation of osazones — was used by Thoday, who found 

 that the sieve-tubes provided the main paths for the removal 

 of free sugars from the leaf. This interesting line of work is 

 still in progress, and the results, already obtained by Thoday 

 promise a large accession to our knowledge of the movements 

 and changes undergone by carbohydrates in the plant. 



Mr. A. S. Home, in a paper on the absorption of water by 

 certain Leguminous seeds, after dealing with some features in 

 the structure of the seed-coats, gave some interesting results 

 of experiments carried out with the assistance of Miss CouU 

 and Mr. Holzapfel. The weights and volumes of swelling 

 seeds were determined at short intervals for continuous 

 periods of twenty-four hours or more, and the beha\iour of 

 each seed represented by a cur\e. The ciir\es obtained for 

 submerged seeds with sealed micropyle, in the case of broad 

 bean for instance, differ considerably from the curves for 

 unsealed seeds ; but it is contended that the use of the 

 micropyle for the admission of water would probably not 

 occur in nature — in every case, at any rate, directly the seed 

 began to absorb, water entered continuously through the seed- 

 coat. Distinctive curve-forms were obtained for different 

 varieties of lupin and for Mendelian peas {e.g., round and 

 wrinkled peas, "bean" pea, "express" pea). It w-as found 

 that the seed-coat in each case (broad bean, runner, kidney 

 bean, and so on), behaved as a semi-permeable membrane, 

 like the coats of barley, and so on. The coat of the white 

 kidney bean gave remarkable results, the column of liquid 

 rising in the tube of the osmometer in three days to a higher 

 level than it did in the case of pig's bladder membrane in 

 seven or eight days under similar conditions. 



Professor Bottomlcy described his investigations on the 

 association of nitrogen-fixing bacteria with the Blue-green 

 Algae iXostuc. Anabacna) found inhabiting the roots of 

 Cycas. the thallus of the liverwort Antlioccros, and the 

 leaves of the Water- Fern Azolla. Cultures made by 

 inoculating nutrient gelatine with drops of crushed Azolla 

 leaves or Antlioccros thallus gave in two days the typical 

 round colonies of Azotobacter and the ovoid colonies of 

 Pscitdonionas, .and these two nitrogen-fixing bacteria were 

 also recognised by staining microtome sections of the plants 

 inhabited by them and by the Algae. It is possible that the 

 association is advantageous to the host plant — the Alga 

 supplying the necessary carbohydrate for the nitrogen-fixing 

 bacteria, and the host plant absorbing some of the nitrogenous 

 product made by the bacteria. 



Two papers on the physiology of Fungi may be noted. 

 (1) Professor Buller dealt with the large club-shaped cells 

 (cystidia) found between the spore-producing organs (basidia) 

 in the gills of the toadstool genus Coprinus. Brefeld had 

 suggested that the use of the cystidia is to act as props to 

 keep the gills from pressing against each other, and this view- 

 is supported by Buller, who adds that the cystidia also serve 

 to provide sufficient space between the gills for the free 

 escape of the spores. The fate of the cystidia is curious — 

 directly they have fulfilled the function of propping the gills 

 apart and keeping the way clear for the falling of the spores 

 from the cap of the toadstool, they undergo self-digestion, 

 their contents being absorbed by the neighbouring cells, and 

 this digestion of the cystidia always occurs before the same 

 fate overtakes the rest of the tissue of the gills. (2) Mr. 

 Lechmere described a species of Saproh'gnia. one of the 

 aquatic Fungi, which had been kept in cultures but had not 

 formed sexual organs and was therefore not named. The 

 cultures were of interest because of the great variety of 

 methods of asexual reproduction observed under different 



conditions — this one plant showed methods of asexual repro- 

 duction which were regarded by earlier observers as charac- 

 teristics of six different genera of the family Saprolegniaceae ! 

 Of the ecological papers read, perhaps that of most general 

 interest was Mr. M. Wilson's account of plant distribution in 

 the woods of north-east Kent. In this district a large pro- 

 portion of the woods is coppice with standards, felling taking 

 place about e\'ei-y fourteen years. There is little \ariation in 

 the altitude, and the plant distribution depends chiefly on the 

 character of the soil. Five types are distinguished : — (1) 

 Beech type on the shallow soils of the Chalk ; standards 

 chiefly beech, nndershrubs yew, oak, hazel, dogwood, spindle, 

 and privet; dog's mercury (Mcrciirialis percniiisi, wood 

 spurge, woolly mullein, and Viola liirta arc abundant. (2) 

 Ash-hazel type on the " clay with flints " on the Chalk ; 

 horn-beam, often found ; oak standards usually present ; 

 mercury abundant, with primrose and bluebell. (3) Chestnut 

 type on the Thanet Sand ; usually coppice with chestnut or 

 oak standards : bramble often present ; on the deeper deposits 

 bluebell abundant, with red campion and moschatel ; woodruff 

 and goldenrod characteristic of this type. (4) Oak-birch- 

 heather type on the Woolwich and Reading Series and on the 

 Oldhaven Pebble-beds ; Scots pine frequently found ; woods 

 usually thin and open ; heather and bracken abundant, with 

 hairy woodrush and sheep's sorrel ; soil usually strongly acid. 

 (5) Oak type on the London Clay; usually coppice with oak 

 standards ; bracken abundant, and many plants found in 

 woods of the preceding type occur. There is usually a sharp 

 distinction between the woods occurring on calcareous soils 

 and those on the Tertiary formations ; in the former the soil 

 acidity is slight or none, and dog's mercury is abundant, 

 while in the latter the soil is acid, and mercury is absent. 

 Woods of intermediate character are found on alluvial 

 deposits and on the edges of Tertiar>- deposits. During the 

 latter years of coppice growth a deep shade is produced and 

 few herbaceous plants occur — including plants little affected by 

 shade and flowering in spring, and dwarf plants persisting 

 in the vegetative state and rarely flowering. During this 

 period there is an increase in the amount of humus 

 and probably a simultaneous increase in acidity. Felling 

 causes a great increase in the light intensity, and the 

 temperature of the surface soil increases, these changes 

 resulting in a great increase in the number of herbaceous 

 plants, including (a) plants which have persisted during the 

 shade period, and many of which now develop luxuriantly, (6) 

 woodland plants unable to exist in the shade period ; these are 

 largely biennial, but a few annuals and perennials are found. 

 The maximum development of herbaceous plants is reached 

 during the third year ; after this they gradually diminish, on 

 account of the increase of shade, and the shade condition of 

 the vegetation is reached by about the tenth year. 



CHEMISTRY. 



By C. ."^iNSWORTH Mitchell, B..^. (Oxon)., F.l.C. 



THE SFKUM TEST FOR BLOOD.— Everyone who has 

 read the account of a recent trial for murder must have been 

 struck by the report of the evidence that certain stains had 

 been proved to be human blood by a " new serum test." 



As this test, now used for the first time in an English 

 criminal case, is an application of one of the most remarkable 

 discoveries in physiological chemistry, an outline of the 

 principle upon which it is based will doubtless interest even 

 those who have no knowledge of the science. 



The discovery dates back to 1898, when Bordet found that 

 the serum from rabbits into which cow's milk had been injected 

 gave a precipitate of casein when added to milk. 



Two years later it was shown by Wassermann and Fisch 

 that the use of the precipitating agents formed in the sera of 

 animals, to which substances he gave the name of precipitines, 

 rendered it possible to distinguish between the milk of different 

 kinds of animals, the milk in each instance only yielding a 

 precipitate with the serum specifically adapted to it. 



A further extension of the method was discovered in 1902 

 by von Rigler (Oestcrr. Client. Zcit, 1902, 5, 97), who showed 



