36 ON GEOWTH AND EXTENSION IN THE VEGETABLE KINGDOM. 



chicken in the egg ; but considering the great number of parts 

 wliich are there to be formed, we may conjecture that for the 

 generation of a thin layer of wood from the cambium, only a very 

 short time is required. With regard to the rapid formation of 

 crystals, I have made a discovery which, as it appears to me, 

 is not unimportant. When a precipitate of lime is produced by 

 a solution of carbonic-acid-natrum, or kali in nitric acid, and the 

 precipitate is immediately brought under the microscope, the 

 liquid is full of little globules, and therefore to the naked eye, 

 where the globules are thickest, turbid. Soon these globules are 

 changed into rhomboids, the ordinary crystallization of carbonate 

 of lime: it is only when the liquid is rapidly dried up that their 

 form does not change. It is sometimes possible to bring the 

 precipitate of a solution of lime in sulphuric acid under the mi- 

 croscope whilst it is still in the form of globules, but they 

 are rapidly converted into crystals as if by a magic wand. I 

 published these and other experiments in a short memoir ' On 

 the Formation of Solid Bodies,' Berlin, 1841. I have since then 

 caused water to freeze under the microscope, and seen how the 

 water first becomes turbid, probably from globules, and soon 

 afterwards the crystals are formed. This observation is made 

 known in Poggendorf's ' Annals.' * 



We must, however, take into consideration the opinions of 

 other writers on the generation and multiplication of cells. 



* Schleiden says, in his ' Elements of Scientific Botany,' vol. i. p. 214, — 

 " In order to prevent false conclusions, I must here remark, that the theory 

 of crystallization proposed by Link, according to which crystals are formed 

 by the union of smaller globules, rests on insufficient observations." I 

 never gave out a theory — I only related my observations, upon which I 

 might rather have been reproached for seeing too much. Again, — " In the 

 first place it would be natural, with a view to observing the generation of 

 crystals, not to choose precipitates for that purpose, which are reckoned by 

 chemists among the so-called tumultuary crystallizations, but to make the 

 first observations on crystals formed by simple deposits in concentrating 

 fluids. Here we may see, for instance, in the case of nitre, ammonio- 

 muriate of platinum, but most beautifully and readily in ammonio-muriate 

 of zinc, &c., that the crystal nucleus appears suddenly, in no appreciable 

 moment of time, in the fluid which is, and remains, perfectly clear, and then 

 grows steadily by additions from without in almost imperceptible pulsations." 

 I have often seen this : the exhibitors who used to go about with solar 

 microscopes showed it ; and it is told in several old manuals of physics, 

 but nothing came from it ; it was necessary to go to work in some other 

 way. Now Schleiden relates, that when we allow two fluids, which between 

 them form a precipitate, to come together under the microscope, a mem- 

 brane is produced, which must necessarily consist of crystals. The mem- 

 brane is a turbid partition, and depends on the nature of the fluids whether 

 the crystals form sooner or later. Whoever makes the above experiments, 

 or those detailed in the memoir above quoted, will find the thing so clear 

 as to leave no doubt. As Schleiden takes the opportunity to rake up this 

 matter, I have thought it allowable to bring him forward on this occasion. 



