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apparent when we consider that in plants, contrary to what obtains 

 among animals, external form itself is often structure, or rather it is 

 equivalent to the internal structure of animals : for structure being a 

 modification of form for the performance of some function in the eco- 

 nomy of the creature, " in animals such modification is usually an in- 

 volution of form, in plants the reverse." 



Naturalists are aware that in the lowest as well as in the highest 

 groups, whether of plants or animals, there is no organ which is equal- 

 ly and uniformly available as affording distinctive characters. " For 

 example, the shape of a leaf in one genus of plants may be common 

 to all the included species, and therefore is not a specific character ; 

 in the next genus it may vary in each species, and the variation be 

 constant in each, becoming the most evident source of distinction be- 

 tween the species." This depends on what Mr. Forbes terms " the 

 law of undulation of character^'' that is, "either on the adaptation of 

 organization to circumstances," or on "modifications of forms &c., of 

 no importance in the animal or vegetable economy, though of great 

 value as marks to distinguish one original fonn (that is species) from 

 another. In the last case, the character is usually also representative ^ 

 that is, it may be the analogue of an organ which plays an important 

 part in some other species, group, or type." 



The author has chosen the genus Viola as affording illustrations of 

 his positions. 



" Among the irregularly-flowered genera of the family of Violarieae, we often find 

 certain of the stamina provided with dorsal appendages, styled by some botanists nec- 

 taries, which are lodged in the spur of the flower. In the descriptions of violets, 

 mention is rarely made of these bodies, they being generally regarded as of generic 

 importance only. Any one, however, who compares the nectaries of a pansy with 

 those of a dog-violet, will see such a difference, as indicates a specific, at any rate, a 

 sectional importance. In order to ascertain the value of the character so derived, I 

 have compared minutely above seventy species of violets ; and the results of such com- 

 parison, and their application to the elucidation of British Botany, I now lay before 

 the Society." — p. 77. 



1. Form of Nectaries. In the allies of V. canina they are lancet- 

 shaped, — the most common form; in the pansies they are linear; 

 and the rarest form is the rotund, found in V. palustris. These ai'e 

 the only three forms in the genus ; the first varies in length and 

 breadth, the linear in length. 



2. Relations of Nectary and Spur. The spur varies in proportion 

 according to the form of the nectaries ; " it is usually thick in 

 proportion to its length, and very blunt," when the nectaries are lan- 

 cet-shaped. " The rotund nectary is associated with a very short 



2f 



