Keith! s Botanical Lexicon. q i 



the more the natural system is expanded, the better it will be 

 understood. The author has given his reasons why he has been 

 induced to offer this scheme to the attention of his readers, and 

 concludes thus : — 



" It is the part of the experienced and practical botanist to reduce classes 

 to orders, or to suborders, if necessary, and to construct their diagnosis; or 

 rather, perhaps, by reversing the process and advancing to the line of ascent 

 to reduce orders and suborders to classes ; and to the experienced and prac- 

 tical botanist we are content to commit the task." 



As a vegetable physiologist, the reverend author stands de- 

 servedly high. The book before us contains almost every thino- 

 which has been written by men of science on the subject; but 

 we look in vain for anything decidedly new. The plain and 

 palpable parts of the science all stand out in sufficiently bold re- 

 lief; but the more obscure parts are left untouched. This is 

 much to be regretted ; because, as Mr. Keith holds possession of 

 the good opinion of the public, he might have made his Lexi- 

 con a standard work, without " spot or blemish." The dark 

 pages of former writers he should have cleared up ; their theo- 

 ries he should either have established or demolished by an ap- 

 peal to practical facts ; and not sent them down to posterity 

 surrounded by the halo of a great name. 



It appears that Mr. Keith is an abettor of the idea that the 

 matured sap is " organisahle : " surely, his chemical knowledo-e 

 (of which he has an ample share) should undeceive him in this 

 untenable doctrine. Can he, as a chemist, really comprehend 

 that any organic structure or membrane, however simple, can be 

 formed of sap in any state in which it is found, or by any change 

 or combination of which it is susceptible ? He unluckily asserts, 

 on the authority of the respectable and venerable Mi-. Knio-ht, 

 that the elaborated sap descends ; while he knows that this, 

 being an invisible process, never has, nor ever can be, proved, 

 and is, therefore, a mere supposition. The only instances cited 

 as proofs are, first, the counter-currents of juices observed in 

 the petioles of leaves by Dawson, Knight, and by the late Mr. 

 Capper of Bath : but the descending portion cannot be traced 

 farther than the base of the petiole ; and to maintain that it sinks 

 all the way to the roots, is a purely gratuitous assumption. The 

 second instance cited as proof is the swelling of a branch above 

 a bandage; but, as the branch also swells below the band, it is, 

 in fact, no proof at all. If a branch be strangled by a wire, the 

 swelling on each side is nearly equal ; but, if with a shred or 

 tape, the protuberance is certainly greater on the upper side. 



Mr. Keith continues to reiterate the notion, that the new 

 alburnum and liber are formed of the descending sap, prepared 

 for that purpose by the leaves. Now, this is again unfortunate ; 

 because he must know that new layers of both alburnum and 



