116 OBJECT LESSONS IN BOTANY 



ences, botanists liave formed a system called the N'atural Sys- 

 tem. Let lis now briefly notice this system of classification. 

 24:6. We have already stated that the plants of the globe 

 are all created in species, and that tliis is the first step in 

 classification. Then, in the second place, the species are 

 grouped into genera. Now the number of species of plants 

 already known is about 100,000, and the genera 20,000. 



247. The third step in our system carries us forward to the 

 Natural Ori ers. These are made up of genera. As we as- 

 sociate similar species to form a genus, so we associate 

 similar genera to form the natural orders. The number of 

 orders described in the Natural System is about three hun- 

 dred. For example, the natural order Crucifirse, or the 

 Crucifers, embraces such genera as Mustard, Cress, Cabbage, 

 Turnip, Kadish, Wall-flower, which every one sees to bear 

 resemblance to each other in many respects. 



248. How then shall we define a natural order % It is a 

 group of similar genera ; or, a group of genera closely re- 

 lated to each other. Therefore, individuals form species ; 

 species form genera ; genera form orders. But how shall we 

 classify these three hundred orders ? 



249. Suppose we take an excursion into the mountains. 

 We walk beneath the forest trees, and among the shrubs. 

 We tread upon the lesser herbs, the matted grasses, and the 

 mosses and lichens which cover the rocks. Everywhere we 

 see plants, and behold the domain of the vegetable kingdom. 



245. Wliat is the subject of tliis Lesson XXX. ? 



246, 247. What is the first step in classification ? the second ? the third ? 

 What number of species known in all the vegetable world ? What number 

 of genera ? of orders ? (Ans. 303.) 



248. Define a natural order. Please review these three steps. 



249. Show how we may divide the vegetable kingdom. 



