Retrospective Criticism. 203 



facts." Now, this is precisely what I might fairly boast of having achieved, 

 either by facts or arguments of my own, or by adducing those of others. For 

 on all the grand physiological topics in botany I have shown what were the 

 earliest theories on the subject, and by whom propounded; as, also, how they 

 came to be superseded by later theories, and these, in their turn, by theories 

 later still, till you come down to the state of the science as it subsists at the 

 present day. Let the reader look at the work itself, and not rest content 

 with Mr. Main's account of it in this respect. Let him turn to almost any of 

 those more abstruse and intricate subjects which have been the ground of 

 theories ; such as the ascent of the sap, and its cause ; the descent of the 

 cambium, and its cause ; the fecundation of the vegetable ovulum through the 

 agency of the pollen ; the direction of the radicle and plumelet ; and the 

 growth and food of the plant, and he will find the proofs of what I now 

 assert ; so that, if it be true, as Mr. Main says it is, that I hold possession of 

 the good opinion of the public, I shall expect my Lexicon to become a standard 

 tvorJc, which he thinks I might have made it by doing what I have just now 

 shown that I have actually done. After so much of preliminary praise, Mr. 

 Main's attack was to me, at first, quite astounding and unaccountable. It 

 looked as if I had inflicted upon him some very aggravated injury. It looked 

 as if I had criticised and denounced his own favourite theory in an unhand- 

 some and unfriendly way. Now, I have done no such thing: but I have 

 done what is worse, I have passed it by in silence. To some men, notoriety 

 is sweeter than even praise : they will put up with your censure, if you M'ill 

 but talk about them. But my apology to Mr. Main for not bringing him upon 

 the stage is, that it was not in my plan to introduce or to criticise any theory, 

 or every theory, but such theories only as had been popular among botanists, 

 or propounded by physiologists of high reputation ; and, above all, such as 

 were intelligible to myself. Now, I have not yet met with any botanist who 

 professes to have adopted Mr. Main's theory; and, for myself, I have only to 

 say that I cannot comprehend it, however much I may think about it. For 

 the main ground and pillar of this novel theory, namely, the indusium, with 

 which Mr. Main seems to be so familiar, and about which he writes so con- 

 fidently, I have never yet been able to catch a glimpse of; and, if Mr. Main 

 may argue from the invisibility of the descending cavibium to its non-existence, 

 so may I argue from the invisibility of the indusium to its non-existence also. 

 I will enter no further into a debate on a subject which is beyond my com- 

 prehension, or throw away time in disproving the existence of a nonentity. 



3. My third fault is, that I am " an abettor of the idea that the matured 

 sap is organisable, while my chemical knowledge (of which he thinks I have an 

 ample share) ought to undeceive me in this untenable doctrine." I do not 

 lay claim to any great share of chemical knowledge; but I have quite enough 

 of it to enable me to discern the possession, or the want of it, in others. The 

 opinions which I hold with regard to the organisable capabilities of the sap, 

 or cambium, I hold in common with all the modern chemists I have ever had 

 an opportunity of conversing with, or whose works I have read ; and I regard 

 the principles of modern chemistry as resting on a foundation that cannot be 

 overthrown. Hence, I decline entering into any controversy with Mr. Main 

 on this subject also. His chemistry is a chemistry sui generis. With him, 

 gases are immaterial bodies, Vv'hicb, like the sap itself, are incapable of being 

 formed into any organic structure or membrane, by any change or combination 

 of which they are "susceptible." (^Illustrations of Veg. Phys., vol. ii. p. 135.) 

 But the gases recognised by modern chemists are all material : they may be 

 compared, and weighed, and measured ; and are convertible, by certain chemi- 

 cal combinations resulting from life, into organised structures. Further, Mr. 

 Main represents me, again and again, as advocating doctrines which I must, or 

 ought to, know to be unfounded ; and of adopting opinions out of pure de- 

 ference to others, which I must, or ought to, know to be erroneous. Now, I 

 think that Mr. Main must, or ought to, know that he has no right to indulge 



