xxv.] BOTANY. 97 



144. Thus in gymnosperms, instead of the nucleus 

 of the ovule containing a simple embryo-sac with 

 one germinal vesicle which gives origin to an embryo, 

 several secondary sacs are formed within the primary 

 one, of which each gives origin to four embryos ; and 

 as some gymnosperms have eight or more secondary 

 embryo-sacs each producing four embryos, it follows 

 that in such cases out of thirty-two commencements of 

 embryos all but one are suppressed. 



XXV. CLASSIFICATION. 



145. The objects of a classification of plants 

 are, to place before the mind, in a clear manner, the 

 relationships that exist between them, and to express 

 these relationships in precise terms, so that they may 

 be communicated orally or in writing, and thus facili- 

 tate and advance a knowledge of plants. 



146. The idea carried out in all methods of 

 classifying plants is derived from the fact, that they 

 appear to be related to one another as are the 

 members of the human race, lineally and collaterally ; 

 and whatever theory may be accepted for the origin 

 of their kinds (species), the results obtained by 

 classifying plants, and the mode of reasoning followed 

 in detecting their relationships, are the same as what 

 would follow were they proved to have descended 

 from one or more common ancestors. 



147. For the purposes of classification a nomen- 

 clature is essential, and that nomenclature is the best 

 which conveys briefly and in expressive terms some 

 distinguishing attribute of the plant or group of plants 



