CHAP, ii.] of Plants. Christian Wolff. 473 



Wolff submitted leaves lying in water containing no air to the 

 vacuum of the air-pump, and saw air-bubbles issue, especially 

 on the under side ; but when he allowed the atmospheric 

 pressure to come into play again the leaves became filled with 

 water, and a piece of fir-wood treated in a similar manner sank 

 after the infiltration. In similar experiments with apricots 

 air issued from the rind and especially from the stalk. Wolff's 

 pupil Thiimmig described similar experiments in his ' Griind- 

 liche Erlauterung der merkwiirdigsten Begebenheiten in der 

 Natur,' 1723, and both continued in this question, as in all 

 their physiological and phytotomical views, faithful adherents 

 of Malpighi, as it was wisest then to be. We must linger a 

 moment longer over Christian Wolff, because he published 

 a few years later a general view of the nutrition of plants in 

 a popular form. Wolff's services in the dissemination of 

 natural science in Germany seem not to have been as highly 

 appreciated up to the present time as they deserve to be ; his 

 various works on natural science, some of which took a wide 

 range and were partly founded on his own observations, were 

 full of matter and for his time very instructive ; they con- 

 tributed moreover to introduce more liberal habits of thought 

 at a time when gross superstitions, such as that of palingenesia, 

 reigned even among men who published scientific treatises in 

 the German Academy of Sciences (the ' Acta of the Leopoldina).' 

 If Wolff's own scientific researches show more good will than 

 skill, yet he had an advantage over many others in a really 

 philosophical training, a habit of abstract thought which 

 enabled him to fix with certainty on what was fundamentally 

 important in the observations of others, and thus to expound 

 the scientific knowledge of his day from higher points of view. 

 For this reason his work which appeared in 1723, ' Verniinftige 

 Gedanken von den Wirkungen der Natur,' deserves recognition. 

 It is a work of the kind which would now be called a ' Kosmos,' 

 and treats of the physical qualities of bodies generally, of the 

 heavenly bodies and specially of our own planet, of meteor- 



