LEEUWENHOEK 219 



Eeverse planting became a favourite diversion in the 

 eighteenth century, and Miller's Gardener's Dictionary 

 gives instructions for practising it. 



The interest of such experiments is not solely prac- 

 tical. It is well-known that brambles, Forsythia, &c, 

 enlarge at the extremities of the rooting branches ; 

 some Aroids, &c. form tubers on their aerial branches. 

 Further investigation may possibly throw light, not only 

 upon the origin of tubers, but also upon that reversal of 

 the sap-current which struck Malpighi as remarkable. 



Minute Structure of Wood 



Leeuwenhoek's figure of a piece of lime-wood cut 

 longitudinally is believed to be the earliest represen- 

 tation of dotted ducts. ^ 



Yeast ^ 



The first microscopic study of yeast-cells was made 

 by Leeuwenhoek. He remarked that they give off 

 bubbles in great numbers, as do crabs' eyes when placed 

 in vinegar, and that many of them are compound, con- 

 sisting of several particles united together ; he did not 

 however discover that the compound globules are pro- 

 duced by budding. Upon a few rapid observations he 

 founded a number of speculations, which are set down 

 without much attempt at verification. Thus he states 

 that not only all yeast-cells, but blood-corpuscles also, 

 consist of six component particles apiece. Finding that 

 a tube of rain-water, when set in a window, contained 

 after a few days green globules, he persuaded himself 

 that these too were almost all sixfold. He concludes 

 that the component particles come from the air. The 



lEpist. 74, Arc. Nat. (1692). Vol. II, p. 302, pi. 289, fig. 19. 

 ^Arc. Nat. (1680). Vol. II, pp. 1-14. 



