116 OBJECT LESSONS IN BOTANY. 
ences, botanists have formed a system called the Natural Sys- 
tem. Let us now briefly notice this system of classification. 
246. We have already stated that the plants of the globe 
are all created in species, and that this 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 
Natvurat 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 Crucifire, or the 
Crucifers, embraces such genera as Mustard, Cress, Cabbage, 
Turnip, Radish, Wall-flower, which every one sees to bear 
resemblance to each other in many respects. 
248. How then shall we define a natural order? Itisa 
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. What is the subject of this 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. 
