Comparative Physiology. ] 99 



paring them together. There will also be found a correspond- 

 ence between plants and animals in the manner of performing 

 the remaining functions of secretion and reproduction, when we 

 come to these. 



He next takes a General Vieio of the Vegetable Kingdom, which 

 he computes at between 70,000 and 80,000 distinct species 

 already existing in collections, and probably as many more still 

 undiscovered. He notices the difficulty of laying down perfect 

 distinctions between the different groups, and fixing distinctive 

 characters. " The Phanerogamia (or flowering) and Crypto- 

 gamia (or fruitless plants), two great primary divisions, are 

 distinguished by the want of vessels in the latter ; being mostly 

 a mass of homogeneous cellular matter, having absorption, cir- 

 culation, and aeration performed by the whole mass. The ferns 

 and mosses, however, belonging to Cryptogamia, have a woody 

 stem, and evident indications of vascular structure, though no 

 true spiral vessels ; there are also some species of Phanerogamia 

 to be found in which spiral vessels cannot be detected." He 

 continues to trace the anastomosing of the difierent tribes with 

 one another, and the difficulty of fixing on any distinctive points 

 of difference, in consequence of the connecting links which run 

 through the whole. The belief that there is no such thing in 

 nature as abrupt transitions is more and more confirmed as new 

 plants are discovered, to fill up what were formerly reckoned as 

 wants. This is a bar in the way of distinct separative definitions 

 of plants, which greatly facilitate the acquirement of names by 

 the analytical method. 



Artificial classification depends more on single characters; 

 natural, on a mass of characters. The natural method is better 

 fitted for synthesis than analysis; the most distinctive analy- 

 tical characters of natural systems are artificial. External cha- 

 racters are most easily discerned, and, in systems of botany, 

 simplicity is greatly promoted by using external characters. In 

 the primary divisions of the natural system of botany, external 

 characters can be traced to correspond with the internal ; they 

 have real distinctions in nature, and appear to be created by 

 nature as independent forms of organised matter. Their pecu- 

 liarities are connected with their whole nature, and not with 

 modifications of particular parts merely. There are, no doubt, 

 connecting links, but they do not confuse, and the distinctions in 

 the primary classes are obvious and easily observed. As we 

 descend, however, in the scale of division, natural distinctions 

 are not so obvious, and the lower divisions of natural systems 

 are in great part artificial. A knowledge of the names of plants 

 is the first and most essential step in botany. We must know 

 the name of a thing before we can speak of it, or understand 

 what is said about it ; for the acquirement and communication 



