Abstract: There are disclosed microcapsules containing a phytotoxic compound of the formula: ##STR1## where x is oxygen or sulfur and R is alkyl, alkoxy, alkylamino, halo, nitro or hydrogen, and the microcapsule walls comprise resinous polycondensates which are crosslinked polyurea, crosslinked polyamide or crosslinked polyamide-polyurea wherein the degree of crosslinking is about 25-100%, the walls are about 10 to about 30% of the total weight of the microcapsules, and the microcapsules have an average size ranging from about 7 to about 25 microns in diameter.

Abstract: A process and apparatus for the automatic correction of the focusing of a microscope in an image plane utilizes two microscope outputs forming two images of the same object in two different planes surrounding the image plane and two matrices with at least one line of N photodetectors receiving the two images. A contrast measuring circuit of each image is associated with each matrix and a comparator of the signals is used for the two contrast measuring circuits. Connected to the output of the comparator is a circuit for the formation of a correction signal and the microscope is focused by the correction signal.

Abstract: The method consists in generating an electrical signal B which is representative of the time-dependent variations in transparency, in generating a pulse at the initial instant of measurement, in carrying out an initial measurement of the slope of the curve at the beginning of the portion which has a steep slope, in comparing at predetermined instants the measured value of the initial slope with the slope of the curve which is representative of the signal B at these instants, in generating a second pulse when the measured slope becomes significantly different from the initial slope, and in measuring the time interval which elapses between the first and second pulses.