ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 217 



(1) fermentations accompanied by oxidation ; (2) lactic acid fermenta- 

 tions ; (3) fermentations yielding mucilage ; (4) butyric acid fermenta- 

 tions ; (5) fermentation of cellulose ; (6) partly unexplained fermen- 

 tations. The fermented substances considered are carbohydrates. Each 

 section comprises an enumeration of the more important organisms, 

 with a short account of their characteristics, and the subsidiary products 

 -of the fermentations. The economic aspect of lactic fermentations is 

 •considered in brief. While mainly intended for chemists, the book is 

 .also adapted for those interested in the subject from a physiological 

 standpoint. 



Root-tubercles of Medicago denticulata and other Leguminous 

 Plants.* — G. J. Peirce has examined the origin, morphology, and struc- 

 ture of root-tubercles, especially on the Bur Clover {Medicago denticulata?). 

 He finds that the tubercle bacteria enter a root-hair by softening or 

 dissolving a small portion of the wall. There is no evidence that they 

 usually enter through broken root-hairs. The proportion of root-hairs 

 infected to the number formed is small ; in one case computed to be 

 i in 1000. The infection thread grows fairly straight through the 

 oortical parenchyma to the layer of cells next outside the central 

 cylinder of the root. The tubercles arise endogenously from the same 

 layer as the lateral roots. We may therefore conclude that they are 

 morphologically lateral roots ; they are formed only as the result of 

 stimulation by bacteria. The author asks whether lateral roots arise 

 as the result of internal causes or external stimuli. The growth of the 

 tubercle is apical, the daughter-cells of a bowl-shaped terminal meri- 

 stem constituting the growing part of the tubercle. There is little or 

 no secondary growth in thickness. Tubercles are largest and most 

 numerous near the surface of the soil. It is possible that perennial 

 Leguminosre form few if any tubercles after their roots have grown 

 •deep into the soil. 



The presence of bacteria in the cells of a tubercle prevents the 

 infected cells from forming starch. Uninfected cells do not attain 

 the size usually reached by infected cells : the larger size of infected 

 ■cells is due to increased pressure, probably also to greater irritation. 

 The bacteria cause the degeneration and almost complete destruction of 

 the nuclei of the cells in which they occur. The infection strands grow 

 definitely, chemotropically, toward the daughter-cells formed by the 

 tubercle meristcm, and seem also to grow definitely toward the nuclei 

 of the cells into which they penetrate. Infected cells soon lose power 

 of division, though not of growth. The relation of the bacteria to 

 their host-cells is parasitism, and it is difficult to understand how the 

 leguminous plant as a whole can profit by an association which is 

 injurious and finally destructive to the cells in which the bacteria occur. 

 Intercellular spaces occur in the tissues of root-tubercles ; and even if 

 they did not it would not be necessary to assume that the bacteria live 

 anaerobically therein, since the tubercle-cells do not live anaerobically. 



Intracellular Toxin of the Typhoid Bacillus. f — A. Macfadyen and 

 •S. Rowland conclude that the typhoid bacillus contains within itself an 



* Proc. Calif. Acad. Set, ser. 3 (Botany) ii. (1902) pp. 295-328 (1 pi.). 

 t Proc. Roy. 8oc, lxxi. (1902) pp. 77- 8. 



