384 Comjoarative Physiology. 



Ing the metamorphoses of organs, as the stamens or carpels 

 reverting to the form of leaf, which may be regarded as the 

 type of them all. In the labiate flowers the suppression of 

 one • stamen and the shortening of two others result merely 

 from a deficiency in the evolution of rudiments, and not from 

 alteration of structure ; as is seen in the snapdragon having 

 sometimes five stamens, and the petals all regularly spurred." 



It is in the discovery of such general laws as those of develope- 

 ment noticed in this section, and of the functions in the follow- 

 ing, that practice is greatly benefited by science. When we 

 understand the methods in which the operations of nature are 

 generally performed, we are often enabled to prevent adverse 

 circumstances from being productive of so much harm, by retard- 

 ing and preventing their effects ; and, vice versa, to promote and 

 advance the action of those circumstances that are beneficial. 

 When we can understand the different functions that the dif- 

 ferent parts of plants perform, and how and where these functions 

 are developed, we shall have obtained a knowledge which, when 

 joined to a proper understanding of the action of the stimulating 

 agents formerly treated of, and of the way in which the food of 

 plants assists in developement, Avill enable us to proceed on 

 correct principles. Much no doubt remains to be done, but 

 much has already been accomplished ; and it is the duty of all 

 practical cultivators to endeavour to understand that much. Did 

 not science teach iis, in its first rudiments, that the spongioles at 

 the extremities of the roots were the true absorbent vessels, the 

 manure might be applied to the stock of the root and become 

 injurious rather than beneficial. As the absorbent vessels in 

 animals are placed in contact with the alimentary canal, so do 

 we find those of plants in contact with the soil, which acts as 

 the stomach for the reception and preparation of their food. 

 Liebig characterises the act of digestion in animals as being 

 principally one of solution, the gastric juice (containing muriatic 

 acid, and the substance similar to diastase, formed from the 

 inner membrane of the stomach), with the oxygen of the saliva, 

 and the heat and action of the stomach, reducing the food into 

 a soluble state ; in the same way as the action of the air, joined 

 to the heat and moisture of the soil, reduces the substances 

 deposited as food into a state fit for absorption. Digestion has 

 been said to take place in the leaves ; had this been the case, 

 however, it would have reversed the normal order of develope- 

 ment, and the above remarks of Liebig restore the order of 

 developement to its normal condition. Digestion being only a 

 preparation for absorption, and not a chemical action, which he 

 distinctly says it is not, prevents the necessity of reversing the 

 order of developement, and placing digestion subsequent to, in 

 place of before, absorption. The aeration of the circulating fluid 



