82 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



Elfving's confirmation of the negative pressure of 

 the air in wood is interesting. Among other experi- 

 ments was the following : A transpiring branch was 

 cut under water, and as rapidly as possible transferred 

 to eosin, and a fresh cut made under the surface of 

 the dye : that a strong " suction" still existed was 

 proved by the taking up of the dye to a height of 

 2\ cm. in the alburnum. He then shows that cut 

 branches, transpiring freely, take up eosin, and that 

 on examining with the microscope, all the evidence 

 (as before) goes to show that the liquid ascends 

 through the cavities. It is interesting to note that 

 in these experiments the medullary rays, the cells 

 of which communicate with the tracheides by means 

 of bordered pits, were coloured deep red by the 

 eosin ; indeed in the upper part the rays had taken 

 all the colouring matter. 



As drying proceeded, the wood lost its conducti- 

 bility, but to the last Elfving found the coloured fluid 

 held in the borders of the pits, whence he concluded 

 that one function of the ring-like border is to retain a 

 capillary drop, so that however threatening the drought 

 may be, the pit membrane retains its moist condition 

 to the last. 



The cacao-butter experiments were then applied to 

 the sclerenchyma strands of the Monocotyledons, which 



