ADAPTATIONS TO EXTERNAL MECHANICAL FORCES. ()87 



thickening are to be seen in the same vesseL In a third kind of vessel it 

 takes the form of a net (e), and it is then called a "reticulated vessel." 

 A fourth kind of vessel is thickened all over the inner surface, except at a 

 ■number of places which give the appearance of holes. It is then called 

 a " punctated vessel " [a). Lastly, in Ferns, a common form of vessel 

 is to have the thickening material deposited in bars. It is then called 

 " scalariform," as resembling a ladder {h). 



These cases will be sufficient for the reader to understand the general, 

 or indeed universal law of Nature, that, whatever strength is required, she 

 at once proceeds to supply it in some way or other as may be best adapted 

 to each individual case. 



Pyrus japonica nivalis. [Journal of Horticulture.) 



