PHYSIOLOGICAL BOTANY. 215 



under the microscope, at the instant of their coming into 

 contact, the sudden formation of a membrane, which 

 separates the two liquids, is seen to occur. On minute 

 examination, 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 are 

 used, until lastly the smallest appear only as points, even 

 with the very highest powers. If the liquids are not dis- 

 turbed, some of the crystals which are formed gradually 

 enlarge on both sides in the liquid ; but if the liquids be 

 mixed, 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 the 

 liquid was perfectly clear." These observations are upon 

 the whole correct ; the so-called membrane is a wall of 

 turbid liquid. As long as it appears like a membrane, it 

 is not composed of crystals, but these are soon formed, 

 and it is then composed of them. A similar turbid wall 

 is also seen when the freezing of water is observed with 

 the microscope. See Poggendorff's Annal., vol. 64 (1845), 

 p. 479. Lastly, " After having made many observations 

 and these with great care, I have arrived at the general 

 conclusion, that every inorganic substance, when passing 

 undisturbed into the solid state, immediately assumes a 

 crystalline form ; most of the so-called pulverulent preci- 

 pitates consist of crystals, and the comparatively minute 

 size of others prevents our giving any opinion upon their 

 form." This is certainly the common opinion. But 

 Ehrenberg was the first to show that many fossils consist 

 of globules arranged in rows, and therefore are not com- 

 posed of crystals, and if the drop of liquid containing 

 the 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 small 

 globules. The pulverulent condition of matter therefore, 

 which, I believe, Weiss is almost the only one to admit 

 as a distinct state, cannot be rejected. That crystals are 



