212 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
planted portion of tissue must be placed in its normal position. If this 
is not observed, coalescence of growth may take place, but with various 
disturbances or distortions, or one part may even exercise a poisonous 
influence on the other. He further arrived at the result that the forma- 
tion of cambium is brought about by local causes, and may be induced 
artificially. 
The author enunciates the following law, — that every living cell of 
the root and stem displays polarity, not only in the longitudinal, but 
also in the radial direction, and has therefore an organic upper and 
lower as well as a right and left half; and that similar poles repel, 
while dissimilar poles attract one another. The root-pole of a cell he 
terms positive, the stem-pole negative. The seat of this polarity is in 
the protoplasm. 
Influence of External Conditions on the Flowering of Plants.* — 
Prof. M. Mobius discusses this subject in detail, his conclusions being 
founded largely on observations of Dr. F. Benecke in Java. 
In relation to their flowering, Prof. Mobius classifies plants as 
(a) monocarpic or hapaxanthic, those which flower only once ; ( b ) poly- 
carpic , those which flower repeatedly. The former may again be either 
(1) annual , or (2) ephemeral (i.e. may bring forth several generations in 
a year, e. g. Stellaria media), or (3) may require more than one year 
to reach the flowering stage ; the last are either biennial, or perennial 
monocarpic (i. e. require a number of years to produce flowers, e. g. 
Agave americana.) Perennial polycarpic plants may either bloom 
year after year, or may produce flowers at regular or irregular in- 
tervals of more than one year. To the latter class belong species of 
Bambusa and the sugar-cane; the latter frequently does not blossom 
for many years in succession, and then, in another year, almost every 
plant will produce flowers, to the great detriment of its sugar-pro- 
ducing properties. With many conifers there is often an interval of 
from two to six years between one flowering and another ; with Bambusa 
as much as thirty-two years has been observed. 
With regard to the conditions which promote flowering, it cannot be 
said that light is essential to the development of the flower, though it is 
to the capacity of the plant to produce flowers, as it has a tendency to 
promote the formation of reproductive rather than of vegetative shoots. 
Epilobium angustifolium will flower only in sunny situations, and the 
brighter the light the deeper is the colour of the flowers. The ultra- 
violet rays of light are the most efficient for this purpose. With many 
plants, an alternation of high and low temperatures, involving a period 
of res*t in the winter, is favourable to flowering. Dryness, both in the 
air and in the soil, is, as a rule, favourable to the production of flowers. 
When a plant has an abundant supply of nutriment, this goes to the 
formation of vegetative rather than of reproductive organs. 
Importance of Humus for Plants.f — Dr. W. Hdveler has investi- 
gated the part played by humus in the nutrition of plants containing 
chlorophyll. Humus, which is always the result of the decay of animal 
or vegetable substances, is of very complicated composition, consisting of 
* Biol. Centralbl., xii. (1892) pp. 609-24,673-87. 
t Jahrb. f. Wiss. Bot. (Pringsheim), xxiv. (1892) pp. 283-316 (2 pis.). 
