NATURAL CLASSIFICiVTION. 



317 



to be led, by the mere similarity of form, to suppose that, 

 tlierefore, the organs are alike, has fallen into a mistake 

 which may give occasion to important errors. 



Experience teaches us, that when, from some peculiarity of 

 structure, a function cannot be performed by the organ com- 

 monly destined for that purpose, another organ supplies its 

 place. As the proboscis of the Elephant performs the part of 

 a hand ; as the tail of the Kangaroo, although fashioned like 

 other tails, serves the animals as a bone ; so in the Acacia of 

 New Holland, the leaf-stalks supply the place of leaves. 

 Thus, also, those leaves of water plants, which grow under 

 the water, are divided in the manner of roots, and seem to 

 perform a similar function. 



175. 



There is yet another law to be understood, to enable us to 

 judge properly respecting the Nature of Organs. In innumer- 

 able instances, there appear forms similar to those which are 

 connected with a definite function, but which do not fulfil 

 that function ; and Nature seems, in these instances, as in 

 the animal kingdom, to produce forms which are completely 

 useless, merely for the sake of a harmonious and symmetrical 

 structure. The appearance of filaments with empty anthers 

 in flowers that are altogether female, and of female parts in 

 flowers wholly male ; the structure of filaments in other 

 forms, where they resemble nectaries,; the false nectarothecas 

 in such Orchideae as have no nectaries ; these all are forma- 

 tions which can only be explained by the law of nature we 

 are now illustrating. 



The third mean of knowing the Nature of an Organ, con- 

 sists in the dissection of its structure ; for which purpose pow- 

 erful magnifying glasses are frequently necessary. If we 

 wish to ascertain the existence of the integument possessing 

 the nature of the calyx, we must observe the continuation of 

 the epidermis with its slits in that integument, (312.) A 

 glandular and fleshy structure determines respecting the na- 

 ture of nectaries, as a multitude of short absorbent warts 

 leads to the belief of the existence of the stigma. 



