PHYSIOLOGICAL BOTANY.

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under the microscope, at the instant of their corning intocontact, the sudden formation of a membrane, whichseparates the two liquids, is seen to occur. On minuteexamination, this membrane is seen to consist of crystals,some of which can be perceived with perfect distinctness,some are seen to be crystals when magnified more strongly,others only when the very highest magnifying powers areused, until lastly the smallest appear only as points, evenwith the very highest powers. If the liquids are not dis-turbed, some of the crystals which are formed graduallyenlarge on both sides in the liquid ; but if the liquids bemixed, a large number of the crystals are instantly redis-solved, others continue to increase in size, and fresh crys-talline nuclei are suddenly formed in spots where theliquid was perfectly clear.” These observations are uponthe whole correct; the so-called membrane is a.wall ofturbid liquid. As long as it appears like a membrane, itis not composed of crystals, but these are soon formed,and it is then composed of them. A. similar turbid wallis also seen when the freezing of water is observed withthe microscope. See Poggendorff’s Annal., vol. 64 (1845),p. 479. Lastly, “ After having made many observationsand these with great care, I have arrived at the generalconclusion, that every inorganic substance, when passingundisturbed into the solid state, immediately assumes acrystalline form ; most of the so-called pulverulent preci-pitates consist of crystals, and the comparatively minutesize of others prevents our giving any opinion upon theirform.” This is certainly the common opinion. PutEhrenberg was the first to show that many fossils consistof globules arranged in rows, and therefore are not com-posed of crystals, and if the drop of liquid containingthe precipitate of carbonate of lime, under the microscope,dries up too quickly, a quantity of powder remains be-tween the rhombohedra, and this entirely consists of smallglobules. The pulverulent condition of matter therefore,which, I believe, Weiss is almost the only one to admitas a distinct state, cannot be rejected. That crystals are