198 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
these points are regarded as indicating that Keteleeria represents an 
archaic type of Gymnosperms. 
Habit of Lemna.* — Mr. H. B. Guppy records a series of observa- 
tions on the growth of Lemna minor , gibba , and polyrhiza under different 
conditions of substratum and temperature. L. minor thrives and fruc- 
tifies quite as well on wet mud as on water. In the winter, the fronds 
of L. gibba are flat, and scarcely distinguishable from those of L. minor. 
L. polyrhiza has also a winter form, consisting of rootless reniform 
fronds; these almost always sink when detached. This species is also 
able to go through all its stages of growth on wet mud. The rise of the 
fronds to the surface of the water in the spring is brought about mainly 
by bubbles of air when their new growth commences. L. polyrhiza 
appears to be functionally unisexual, though structurally herma- 
johrodite. 
Exotropism of the Root-system.f — Dr. F. Noll asserts that the 
direction of growth of the ultimate branches of the root is determined, 
not only by geotropism and heliotropism, but also by their tendency to 
grow in a direction radial to that of the mother-root, in other words, by 
exotropism. This is in fact the principal factor in bringing about the 
distribution of the finer roots through a large extent of soil, by which 
they are enabled to absorb the largest amount of nutritive materials. 
This tendency is independent of external influences, and was demon- 
strated by the author by artificially causing root-branches to grow in a 
different direction, and then removing the obstruction, when they at 
once again began to grow in a direction radial to the mother-root. This 
law has also a strong influence on the place of origin of new roots, 
which is always on the convex side when the mother-root is curved. 
Influence of Worms on the Growth of Rhizomes.t — Herr P. E. 
Muller describes the mode of growth of those plants which are provided 
with rhizomes, especially in beech-forests, and the way in which this is 
influenced by the action of worms. This takes place chiefly by the 
loosening of the soil, and the consequent increased power of the roots to 
strike downwards. Aerial stolons with normal leaves thus become re- 
placed by underground rhizomes. 
Assimilation of 'Nitrates by Plants. § — M. Deraoussy finds that 
nitrates are absorbed by seeds from the soil in proportion to the amount 
of nitrogenous substances which they contain. Thus small seeds, like 
those of clover and colza, absorb but a small quantity of nitrates, while 
larger seeds, like those of maize, absorb larger quantities, which are 
found in the seedling. The nitrates thus absorbed appear to be employed 
directly in the formation of the albuminoids necessary for the life of the 
plant. 
Absorption of Free Nitrogen by Plants.|| — Further experiments on 
this subject lead Herren F. Nobbe and L. Hiltner to the conclusion- that 
* Journ. Lmn. Soc. (Bot.), xxx. (1894) pp. 323-30. 
f SB. Niederrhein. Gesell. Nat. u. Heilkunde Bonn, 1894, pp. 34-6. 
t Overs. K. Dansk. Yidensk. Selsk. Forhandl., 1894, pp. 49-147 (20 figs.) and 
pp. xii.-xxxvii. (French resume). 
§ Comptes Kendus, cxix. (1894) pp. 868-71. Cf. this Journal, 1894, p. 469. 
II Landwirthsch. Versuchsstat., xlv. (1894) pp. 155-9. See Bot. Oentralbl, 1894, 
Beih., p. 467. Cf. this Journal, 1894, p. 479. 
