18f) 



KNOWLEDGE. 



May, 1911. 



BOTANY. 



By Professor 1'. Cavers. D.Sc. F.L.S. 



".SOIL WAX" .AND SOIL FKRTILITV.— In the first 

 of a series of papers entitled " Contributions to our Knowledge 

 of Soil Fertility" (Proc. Linn. Soc, A'. S. Wales. 1910). 

 Grei.s;- Smith gives an interesting account of observations on 

 the action of wax-solvents and the presence of thermolabile 

 bacterioto.xins in soil. Water extracts from soil a substance 

 which is toxic to bacteria, the toxicity of the extract being made 

 evident by the retardation of growth, or even the destruction 

 of the bacteria. The toxin is destroyed by heat, by sunlight, 

 and by storage ; it slowly disappears from air-dried soil, and 

 rapidly decays in aqueous solution ; it is not destroyed by 

 salts such as sodium chloride or potassium sulphate. Soils 

 vary in the amount of toxin they contain, good soils containing 

 less, poor soils more. The particles of soil are covered or 

 " waterproofed " by soil-wax, or " agricere," and various wax 

 solvents such as volatile disinfectants increase the fertility of 

 the soil by removing this " waterproofing," when the nutrient 

 substances in the soil are more easily dissolved by soil-water 

 and attacked by bacteria. 



From the results of Greig-Smith's worl<, it is clear that the 

 problems of soil fertility are very far from being solved yet. 

 Doubtless further research will throw light upon such questions 

 as the origin of the toxins and of the soil-wax. whether or not 

 the protozoa occnrrin.g in soils have any real importance in 

 soil fertility, and so on. 



GK.AFT HYBRIDS AND C H I M A FKAS.— Some 

 remarkable discoveries have been made during the last few- 

 years as the result of research on "graft hybrids" and 

 allied forms. 



Until 1907, only three so-called graft hybrids were known. 

 The most familiar is Adam's Laburnum iLabuniuni Adaiiii). 

 obtained in 1825 by M. Adam, a F'rench horticulturist. Adam 

 grafted Cytisiis piirpnrcus. a small tufted species, on the 

 connnon Laburnum, and obtained a shoot with intermediate 

 characters, which was readilj' propagated by grafting and 

 by cuttings, and has long been in cultivation. .A second 

 remarkable form is " Crataegomespilus," supposed to be a 

 graft hybrid between the hawthorn Crataegus nioiiogyna a.nd 

 the medlar Mespihis gennaiiica : the original tree is said to 

 exist still in Lorraine. The third case is that of the Bizzaria 

 orange, believed to have arisen through the inter-grafting of 

 Citrus Atirantium and Citrus inedica. 



In 1907. Winkler (Be;-. deutscU. hot. Gcs., Band 25) 

 grafted a scion of Solanuiu uigrKiii (the common weed, 

 black nightshade) on S. Lycvpersicuiii (tomato), and after 

 growth was resumed, a transverse cut was made across both 

 stock and scion, in the hope that adventitious shoots would 

 grow from the cut surface along the line of contact of stock 

 and scion. Such shoots did actually appear, and in one case 

 the new shoot involved tissues of both stock and scion, 

 but this was clearly not a graft hybrid — one side of the 

 shoot was Solauutu nigruiii and the other was Solanuni 

 Lycopersicuni .' To this peculiar structure, Winkler gave 

 the name "Chimaera"; so sharply marked was the line 

 between nightshade and tomato that some leaves were partly 

 of one species and partly of the other. 



In 1908 (Ibid., Band 26) Winkler obtained an apparently 

 true graft hybrid, which he named Solauutu tuhingcnse. 

 Out of about two hundred and seventy grafts between 

 tomato and nightshade, there arose over three thousand 

 shoots, among which there were five chimaeras and the 

 supposed graft hybrid Solanuni tubingense ; the latter, 

 while intermediate in character, is rather closer to the 

 nightshade than to the tomato. 



In 1909 Winkler iZcitschr. fiir Bot.), obtained several 

 further " graft hybrids " by using the same methods. To 

 the four varieties of these forms he gave the names Solanuni 

 DarK'inianuni, S. Gaertnerianuni, S. proteus, and .S. 

 Koelreutcrianuni ; the first two resemble the nightshade 



more than the tomato, the last two arc closer to the tomato. 

 Some of the new forms appeared as branches from chimaeras; 

 some of them arose several times in the cultures. In a more 

 recent paper iZeitschr. fiir Bot. 1910), Winkler has reported 

 the results of a study of the progeny of these new forms, with 

 some interesting details. The vegetable shoots seem able to 

 fuse and merge readily in \arious ways, yet the tomato and 

 nightshade cannot be hybridised sexually. The " graft 

 hybrids " without exception revert to the nearer parent, the 

 seedlings of ,S. tubingense, S. Dam-inianuni. and S. 

 Gaertnerianuni being always S. nigrum, while the seedlings 

 of S. proteus and S. Koclreuterianuni always are S. 

 Lycopersicuni. The new forms may be hybridised sexually 

 with the nearest parent form, the progeny being pure night- 

 shade or tomato as the case may be. Moreover, reversion in 

 the vegetative shoots is always to the nearer parent form. It 

 is to be noted that the behaviour of the new Solanuni forms 

 is exactly like that oi Laburnum Adanii. which often shows 

 vegetative reversion to one of the parent forms, and whose 

 seeds give rise not to L. Adanii but to L. vulgare. 



Before proceeding to consider the interpretations of these 

 very remarkable results, we may briefly summarise some still 

 more extraordinary discoveries made by Erwin Baur, In 

 Baur's first paper iZeit. Abstr. Vercrbuiigslehre. Band 1, 

 1909) he described the minute structure of geraniums with 

 white-edged leaves (gardeners' " albo-marginate varieties"), 

 and found that the green cells and the colourless cells are 

 each descended from others of their kind, the external 

 portions (comprising two or three rows of cells) being colour- 

 less and the internal portions green, and the limits between 

 them very sharp. Since the sexual cells are derived from the 

 external white layers, the seedlings give pure white forms. 

 White branches give only white forms vegetatively, and green 

 branches green forms only. If a pure white and a pure green 

 be hybridised sexually, there arise green-white mosaic forms 

 in addition to pure white and pure green forms. If in the 

 miisaic forms the growing-point is situated on the line between 

 the white and green portions, there results a chimaera. such 

 as Winkler obtained so often in Solaiiiiiii. In a cross section 

 of the stem the two components appear as sectors, hence Baur 

 calls such forms sectorial chimaeras. For the condition 

 found in an ordinary Pelargonium with white-edged leaves, 

 Baur proposed the term periclinal chimaera. one of the 

 components investing the other ; the growin.g-point is peri- 

 clinally divided into white and green cells, the white being 

 outermost, so that the entire plant consists of a body of green 

 geranium invested by a mantle, two or three cells deep, of 

 white geranium ! 



In a recent paper, Baur (Bio/. Ccntralbl., Band JO, 1910) 

 notes his discovery that " Crataegomespilus " is a periclinal 

 chimaera, consisting of a Crataegus body with a Mespihis 

 investing layer either one cell in thickness (epidermis) or two 

 cells deep. Baur solves the riddle of Laburnum .Adanii, 

 finding that it also is a periclinal chimaera, with an epidermis 

 of Cytisiis purpureiis covering a body of Laburnum 

 vulgare : seedlings, are always the latter, simply because the 

 hypodermal layer, which produces the sexual cells, is of that 

 species ! When the outer layer consists of two or more 

 layers of cells, the seedlings are of the peripheral species, 

 as in Pelargonium. 



Baur's astonishing discovery was almost anticipated in 

 1S95, by Macfarlane (7";-<7/(s. Royal Soc. Ediiibiirgli. \'ol. J7), 

 who made a careful anatomical study of Laburnum .Adami 

 and in his figures showed clearly that this form agrees with 

 Cytisiis purpureiis as to its epidermis and with Laburnum 

 vulgare as to its internal tissues, Macfarlane, however, did 

 not appreciate the meaning and importance of his own 

 observations. In one of his latest papers, Winkler has 

 re-investigated his Solanuni forms in the light of Baur's 

 epoch-making work, and finds that for the greater part they 

 are, as Baur had suggested, periclinal chimaeras. Winkler 

 supposes that what have been taken to be graft hybrids may 

 be actual graft hybrids, resulting from fusion of the cells of 

 different species ; or they may have a hybrid nature owing to 

 the migration between stock and scion of various substances 



