600 Retrospective Criticism. 



application of food of the most nourishing description. Oxymuriatic acid has 

 been tried with much the same results, in the proportion " of a teaspoonful to 

 a gallon of water." (p. 188.) 



Finding, upon the whole, much that is interesting, it may reasonably be ex- 

 pected that some parts of the work should be found open to remark. In 

 tr'iating on the causes of failures and the remedies, it appears to me that the 

 author is too sanguine in his ideas, speaking more in the language of a mecha- 

 nic who perfectly understands all the springs and movements of a piece of 

 mechanism, than of one treating upon organisation, possessed, it is true, of the 

 most perfect mechanism, but mechanism regulated in all its movements by a 

 principle of life, the effects of which are so varied, as to lead to the conclusion 

 that almost every individual is regulated by a system of its own. It likewise 

 appears to me that the author is wrong in some of his ideas, or has got so 

 bewildered in them, as to expose himself to the charge of inconsistency. In 

 illustration of this, I may advert to one of his favourite theories ; namely, that 

 the different parts of a plant possess the power of decomposing their food, and 

 of throwing off the excess, as excrement, by the leaves. He states that, of the 

 four elementary substances of which plants are composed, oxygen, carbon, 

 hydrogen, and earth, " as oxygen is the only element whose existence in excess 

 would create disorder, the leaves have the power of expelling it in the form of 

 gas when exposed to the sun : all the hydrogen, carbon, and earth, not wanted 

 for other purposes, are employed in the formation of leaves," &c. I will 

 not dwell on the seeming inconginiity of making the leaves depend, as it were, 

 upon chance for their developement, when no more hydrogen, carbon, &c., are 

 wanted for other purposes. I will not even attempt to prove that, besides oxy- 

 gen, hydrogen might also be expelled as an excrement, if not directly, at least 

 indirectly, as a component part of the water thrown off by the process of per- 

 spiration (an office of the leaf which the author, professing to teach us what is 

 necessary of vegetable physiology, either does not believe, or has wholly over- 

 looked) : what I want is, a reconciliation between the statement, again and again 

 repeated, that it is not necessary the leaves should expel any principle, save 

 43xygen, and, consequently, that they do not do so, with what is stated in p. 83., 

 that leaves expel immediately oxygen and carbonic acid gas. Again, the 

 author has discovered that no healthy production of plants contains nitrogen ; 

 therefore the application of nitrogen must be prejudicial : but, if this be correct, 

 what becomes of the nitrogen contained in the animal substances employed as 

 part of the food of plants ? It combines with hydrogen, forming ammonia ; 

 which, being lighter than the atmosphere, passes through it. But still there is 

 another query : nitrogen is a constituent principle in our atmosphere ; and air 

 is said to be essential to plants : when they imbibe it, what becomes of the 

 nitrogen which it contains ? Our author has his answer ready, dignified, too, 

 with the name of" proof; " that, as no healthy production of plants contains 

 nitrogen, therefore plants do not imbibe air. (p. 85.) I make no remarks upon 

 such a proof, or on the seeming anomaly, that beings should possess the power 

 of exhaling, but none of inhaling. I confess my ignorance of the use of nitro- 

 gen in vegetation, although it is extremely probable it acts as a moderator of 

 some more active principles, and merely express a hope that, in future, authors 

 will not deem it more philosophical to erect a theory to suit a present pur- 

 pose, than honourable to confess that ignorance which, in all likelihood, we 

 shall ever feel in relation to many of the phenomena of nature. 



It will already be apparent that I do not agree in some of the author's ideas 

 respecting the functions of the different parts of plants ; as, for instance, in his 

 avowal that roots are necessary to the production of leaves, but that leaves 

 are not necessary to the production of I'oots j which, he says, is proved by a cut- 

 ting without leaves put into the ground protruding its roots before it does its 

 leaves (p. 134.); a proof which may be classed with the non-imbibing air pro- 

 perties of vegetables, or my observation must have been very erroneous. It is 



