ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
369 
Rapidity of Growth.'* — Herr F. Benecke has measured the rate of 
growth of the leaf-sheath of Musa sajoientum in Java in May. He found 
the most rapid growth to be between 7 • 40 and 7 * 45 a.m., when the in- 
crease was at the rate of 1 * 1 mm. per minute. This is higher than any 
rate of growth recorded by Pfitzer, except in the case of the filaments of 
Triticum. 
Relation between Tension and Growth in Length.*]- — By experi- 
ments on a considerable number of woody and herbaceous plants, Prof. 
S. Schwendener and Herr G. Krabbe have tested the correctness of 
Sachs’s and de Vries’s theory that the growth in length in any organ is 
a factor of the degree of tension in the cells which compose it. Their 
results are in all cases unfavourable to this conclusion. The observa- 
tions were made on roots, internodes of stems, leaf-stalks, and flower- 
stalks. They find that the growth of an organ may vary greatly with 
the same turgor-tension ; in the cases where the increase in length is 
distributed over a large space, there is neither any zone of maximum 
growth nor any zone of maximum turgor-tension. Not unfrequently 
zones of rapid growth have a low degree of turgor-tension, and vice versa. 
The growth in length of an organ is dependent on other factors which 
have much more influence than the degree of turgor-tension, such as the 
production of the formative substances, their adaptation for the formation 
of the cell-wall, their chemical transformations, &c. 
Periods of Growth and Causes of Development.^ — Prof. J. Sachs 
argues that a large number of morphological facts may be correlated and 
explained by a methodical study of the phases of the growth of the 
plant in relation to the external causes of or incitives to development 
( Bildungsreize ). It must be regarded as an axiom that every new 
organ is a product of those already in existence. 
Four phases of growth may — somewhat roughly and arbitrarily — be 
distinguished in any organ ; its embryonal condition ; its emergence 
from the growing point ; its growth in length ; and its maturity. The 
first two may be regarded especially as morphological, the last two as 
physiologico-biological periods. The third period is the one in which 
the organ is especially sensitive to influences of a purely mechanical 
nature, — light, gravitation, pressure, contact, &c. ; the fourth is charac- 
terized by the activity of chemical processes in the cell-walls. 
Some help is given to arriving at a true theory of growth by a 
study of the phenomena of abnormalities. It is during the embryonal 
condition that the substances of which the flowers are formed travel 
from the leaves to the rudimentary floral organs ; and abnormalities 
may result from some of these molecules taking a wrong way in their 
distribution through the microscopically small organs ; or arriving too 
late or too soon. The highly organized and differentiated forms of galls 
resulting from the punctures of insects are also very instructive in this 
respect. 
Growth of the Fruit of Cucurbita.§ — Mr. F. Darwin has made a 
number of observations on the rate of growth of the fruit of various 
* Ber. Deutsch. Bot. Gesell., xi. (1893) pp. 473-6 (2 figs.). 
t Jahrb. f. wiss. Bot. (Pringsheim), xxv. (1893) pp. 323-69 
X Flora, lxxvii. (1893) pp. 217-53. § Ann. Bot., vii. (1893) pp. 459-87 (2 pis.). 
1894 2 c 
