104 NATURAL METHOD. 



3. POLYGAMIA FRUSTRANEA : has the florets of the disk per 

 feet; those of the ray without either stamens or pistils 

 which are well formed. Example, the sunflower. 



4. POLYGAMIA NECESSARIA : has the florets of the disk with 

 stamens only, the stigmas being imperfect ; and those of 

 the ray with pistils only. Example, silphium. 



5. POLYGAMIA SEGREGATA : has all the florets perfect, and each 

 floret has a well formed calyx, the whole being enclosed in 

 an involucre. Example, elephantopus. 



The orders of the 20th, 2 1st, and 22d classes are for the most 

 part characterized by the number of stamens. 



18. The 23d class, Polygamia, has three orders founded on 

 the immediately preceding orders. 



1. MONOECIA has both separated and perfect flowers on the 

 same individual. 



2. DICECIA : when one individual bears the perfect, and another 

 the two kinds of separated flowers. 



3. TRHECIA : when one bears the perfect,' a second the stami- 

 nate, and a third the pistillate flowers. 



The Ferns, Mosses, Algse, Fungi, &c., constitute the orders 

 of the 24th class, Cryptogamia. 



19. The basis of the natural method was proposed by a 

 French botanist, Bernard de Jussieu, and this classification, per- 

 fected by the labours of Antoine Jussieu (pronounced jus-sue), 

 and the botanists of his school, is the one now generally adopted. 

 According to this classification, we bring together, in groups 

 called genera, all the species of plants which resemble each 

 other throughout, in the important characters of their organiza- 

 tion ; and in the same manner we bring together, into divisions 

 of higher rank, named natural families, the different genera, 

 the most essential organs of which possess an analogous mode 

 of structure : then we group together the natural families accord- 

 ing to the same principle, and finally obtain a small number of 

 divisions which comprise all the subdivisions we have mentioned 

 above, and which, by their union, include the whole vegetable 

 kingdom. 



20. The most important differences among plants, consist in 

 the absence or presence of flowers or organs of fructification, 

 and this difference almost always coincides with their peculiar 

 modes of organization in all their parts, such as the absence or 

 presence of distinct vessels in the tissue of the plant. There- 

 lore, in a natural method, we must first divide the vegetable 

 kingdom into two groups ; one containing plants which are re- 

 produced by means of flowers, and the other including plants 



18. What are the orders of the class Polygamia? 



19. What is the basis of the natural method of arranging 1 plants ? 



JiO. What are the most important differences among plants? Into how 

 many groups is the vegetable kingdom d'vided ? What are they ? 



