ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
513 
influence of tlie transpiration of the leaves showed a nearly uniform 
tension of from 3/4 to 4/5 atmospheric pressure. The water in the 
interior of the tracheids did not form an uninterrupted column from the 
base to the summit of the stem ; the masses of water were separated from 
one another by bubbles of air. From the communication between 
columns belonging to adjoining “Jamin’s chains,” masses of water 
occur, of limited size and number, interrupted only by the very permeable 
membranes of the bordered pits. Our knowledge of the physical 
properties of these membranes is not sufficient to enable us to form a 
satisfactory theory of the function of the bordered pits. The chemical 
composition of the imprisoned air could not be determined with 
certainty. 
C3) Irritability. 
Photometric Movements of Plants.* — Herr F. Oltmanns records a 
series of observations on the movements of plants, or of parts of plants, 
dependent on light, — those especially observed being Volvox globator , 
Spirogyra , Vaucheria , Phjcomyces nitens , leaves of Phaseolus, Bobinia , 
Tropseolum, &c. The phenomena of phototaxy he divides under two 
heads — “ orthophototaxy ” ( Volvox , Spirogyra) and “ plagiophototaxy ” 
(movements of chlorophyll-bodies). By this latter term is meant the 
power of light to effect changes in position when falling at any angle 
between 0° and 90°. The phenomena of phototropy — i. e. positive or 
negative heliotropic movements— are, in the same way, classed as 
“ orthophototropic ” ( Vaucheria, Phycomyces, shoots of flowering plants) 
and “ plagiophototropic ” (leaflets of Bobinia pseud acacia, Phaseolus 
multiflorus , Tropseolum majus). For every plant or every organ of a 
plant there is an optimum intensity of light during the period of its 
active growth ; and the object of all photometric movements appears 
to be to bring the plant or the organ under this optimum degree of 
illumination. 
The author points out the remarkable resemblance between photo- 
metric and all other movements of irritability, such as the chemotactic, 
thermotropic, and hydrotropic. Movement occurs, in all these cases, 
only when there is considerable departure from the optimum on one 
side only of the organism or of the organ in question, or when on both 
sides there is a departure but in very different degrees. 
Carpotropic Movement in Trifolium subterraneum.f — Dr. H. Boss 
describes the process by which, in this species, the young fruits become 
buried in the ground. As soon as the fertilization of the fertile flowers 
has been accomplished, the common peduncle of the inflorescence curves 
so as to bring to the surface of the soil the young fruits which are 
surrounded and protected by a ball of sterile flowers consisting only of 
an elongated and very hairy calyx. By the continued growth of the 
peduncle, accompanied by circumnutation, this ball buries itself in the 
soil, where the seeds ripen. The cause of these movements of the 
peduncles is negative heliotropism ; they always tend to move away 
from the light. The flowers appear to be self-pollinated. 
* Flora, lxxv. (1892) pp. 183-266 (1 pi.), 
f Malpighia, v. (1892) pp. 304-11. 
2 N 
1892. 
