60 
SUMMARY OP CURRENT RESEARCHES RELATING TO 
the expense of the protoplasmic contents of the cell. At the apex of 
the root-hairs they form botryoid colonies, which surround themselves 
with a refringent membrane, and coalesce with the cell-wall of the root- 
hair. From this period until the tubercle is fully formed, the growth 
of the bacterium-tube resembles that of a fungus-hypha, penetrating the 
epiderm and the cortex of the root even as far as the endoderm of the 
central cylinders. The neighbouring cells now begin to increase by 
division ; while the bacterium-tubes branch abundantly, and form the 
“ bacterioid tissue.” The position of the tubercle is not a definite 
one, but may be opposite either the xylem of the central bundle, or the 
phloem, or between the two. 
The relation between the root and the bacterioid organism is a 
true symbiotic one, each developing more vigorously at the expense of 
the other ; though whether the additional supply of nitrogen is derived, 
as Hellriegel supposes, directly from the atmosphere or not, the author 
has been unable to determine. Finally, the contents of the bacterioid 
cells become gradually absorbed by the host-plant ; this taking place 
with greater energy in inverse proportion to the amount of nitrogen 
supplied from the soil. The host-plant, therefore, is the stronger of the 
two symbiotic elements. 
Tubers of Hydrocotyle americana.^ — Mr. T. Holm describes in 
detail the vegetative structure of this American marsh-plant, especially 
of the little-known tubers attached to the underground stolons. The 
plant has two kinds of vegetative propagation, — by these stolons which 
end in tubers, and by runners which creep along the surface. 
B. Physiology. 
Cl) Reproduction and Germination. 
Heredity and Continuity of Germ-plasm.-f — Herr G. Liebscher 
describes a series of experiments on hybrid barleys, especially between 
the 2-rowed and the 4-rowed forms, from which he draws conclusions 
favourable to Weismann’s theory of the continuity of the germ-j^lasm, 
at least as far as its substance is concerned ; though its structure may 
be independent of this ; the structure not determining the properties 
themselves, but only their manifestation or latency. 
Pollination by Insects.^ — M. J. M‘Leod describes the mode of 
pollination of a number of flowers belonging to the Belgian flora ; and 
gives many particulars with regard to the relative importance of the 
part played by different classes of insects in the fertilization of flowers. 
The following is given as the order of importance : — Coleoptera, hemi- 
tropous Diptera (Syrphidse, ConopidaB, Bombylidae), Apidae with long 
proboscis, Lepidoptera. 
Fertilization of Gladiolus.§ — M. 0. Musset describes certain curva- 
tures of the styles and filaments of Gladiolus segetum, in consequence 
of which, notwithstanding the extrorse dehiscence of the anthers, self- 
* Proc. U.S. National Museum, 1888, pp. 455-62 (2 pis.). 
t Jenaisch. Zeitschr. Naturw., xxiii. (1889) pp. 216-32. 
j Bot. Jaarb. (Gent), i. (1889) pp. 19-20 and 100-23 (3 pis.). See Biol. 
Centralbl., ix. (1889) p. 257. § Comptes Eeiidus, cviii. (1889) pp. 905-6. 
