iv.] VARIOUS THEORIES, &c. 129 



Now it is allowed universally that in a living cell 

 there must be continually recurring splittings of com- 

 plex to simple bodies, and re-combinations of simple 

 bodies into complex ones ; oxidations of organic 

 molecules to carbon dioxide and water ; transforma- 

 tions of soluble into insoluble substances, and so on. 

 Whence we have only to assume a certain regularity 

 or periodicity of these processes to have all that is 

 necessary for the hypothesis. 



If this is given, we have at the same time an explan- 

 ation to account for the facts that the sap from a 

 bleeding stump is more dilute than that in the cells ; 

 that the root-pressure is so powerful ; that old roots 

 may be made to exhibit root-pressure. 1 



If now we take the case of the Conifers, it also 

 explains in a very simple manner the histological 

 peculiarities of the wood. On a transverse section 

 of the stem of a Conifer, any medullary ray-cell, 

 which is in contact above and below and at both 

 ends with similar cells, has a radial row of tracheides 

 on its flanks, and these tracheides have particularly 

 large and open bordered pits on the sides next the 

 medullary ray-cell, water passing easily from cell to 



1 I would also suggest that it may explain the periodicities observed 

 in the out-flow from a cut stump. 



K 



