216 PHYSIOLOGICAL BOTANY. 



not at once formed in the liquid, but that a nucleus is 

 first suddenly formed from a liquid, which subsequently 

 increases in size, my observations upon precipitates have 

 shown distinctly. 



The author's remarks (p. 53 et seq.) upon the produc- 

 tion of the various forms occurring in nature are upon 

 the whole correct and to the purpose. The form either 

 excludes the mother-liquid, i. e. the formative fluid, during 

 its production, or it incloses it. The first is the case in 

 inorganic, and the latter in organic bodies. I should not 

 say, that the crystal during its formation excludes the 

 formative fluid, for the entire globule, or the entire aggre- 

 gation of globules, in the above experiments is transformed 

 into the crystal. Moreover, this consideration appears 

 to contradict the author's own opinion upon crystalliza- 

 tion, according to which the crystal is at once formed in 

 the liquid, and during its increase merely withdraws 

 particles from the formative liquid. But it is certainly of 

 great importance that organic bodies should be formed 

 within an envelope, where external agencies are directed 

 towards the centre of the formative liquid. When the 

 author says : " We thus characterise the idea, organism, 

 as the relation of the figure or form to the inclosed 

 mother-liquid, and life as the reciprocal action exerted 

 between the mother-liquid and the form," he must, on a 

 little reflection, understand how very unsatisfactory are 

 these characteristics. It was, therefore, with satisfaction 

 that I read the author's remarks (p. 64 et seq.) upon 

 Minerals, Plants, and Animals. They contain if he will 

 not take it unkindly a poetical effusion, which if it does 

 not distort the facts, forms an agreeable embellishment 

 to the subject. 



The treatise on the Microscope (p. 82 et seq.) may be 

 strongly recommended to those who make use of this 

 instrument, although I find the following passage at the 

 end of it (p. 105) : "It is considered that little more is 

 required to make a microscopic observation than a good 



