CHARACTERS OP NATURAL SYSTEM. 347 



whilst in the orders especially characterized by it, there is pro- 

 bably not a single genus in which it is absent. It must be 

 remembered that albumen exists in all seeds at an early period 

 of their formation; and that the subsequent difference will depend 

 upon the degree in which it is absorbed by the embryo. 



501. The student, who has given attention to the preceding 

 statements, is not unlikely to feel some perplexity, on account of 

 the constant uncertainty which has been stated to attend the 

 value of the several characters that have been enumerated. But 

 as he proceeds further, he will find that this uncertainty is greater 

 in appearance than in reality; and that it necessarily results 

 from the properties of a Natural Group, as already described. 

 In dividing the Vegetable Kingdom on an Artificial Method, it 

 seems very easy to lay down a small number of characters as the 

 standard ; and to bring together, or to separate, Plants, according 

 to their conformity or variety in these. But, as has been, already 

 shown, when we come to apply this plan, numerous difficulties 

 are met with, in consequence of the differences which are of 

 constant occurrence, among plants belonging to the same genus 

 or even to the same species (. 481); so that even here, the 

 Botanist must be guided by general resemblance. Now, although 

 it is quite true that no single characters, when traced throughout 

 the Vegetable scale, can be relied on, as indicating the Natural 

 Affinities of plants, yet experienced Botanists have little difficulty 

 in defining each order, by a certain combination of characters 

 which are peculiar to it; and not unfrequently, the plants 

 belonging to one order may be separated from those of all other 

 groups, by some evident and well-marked peculiarity. 



502. On the foregoing principles, the class of EXOGENS is 

 divided by De Candolle in the following manner. 



The first group consists of those, of which the Flowers possess 

 both calyx and corolla, and in which the petals of the latter aie 

 distinct, and which are therefore Polypetalous. This group is 

 divided into two Sub-classes, according to the mode of insertion 

 of the stamens. 



