xvi Life and Living Creatures 309 



of natural groups, the members of which show a regular 

 advance in complexity of structure. Between the simplest 

 groups of each kingdom it is difficult and often impossible 

 to trace any difference. All living creatures are termed 

 organisms, and the science which takes account of them 

 with special regard to their common characteristics is 

 termed Biology (literally Life-lore). The classification and 

 life-history of plants are the objects of the department of 

 Biology known as Botany, while the department known as 

 Zoology is similarly occupied with the study of animals. 



396. Classes of Plants. Botanists group plants into 

 sub-kingdoms, classes, natural orders, genera, and species. 

 A species includes all the individual plants, which are so 

 much alike as to make it certain that they are descended 

 from the same stock and which are mutually fertile. A 

 genus includes a group of species closely related to each 

 other. A group of related genera forms a family, a number 

 of allied families forms an order, and the orders are them- 

 selves grouped in classes. Thus, for example, in the class 

 of Dicotyledons there is an order called Ranunculacese, 

 which includes several families and many genera, amongst 

 others that of Ranunculus, which in turn includes many 

 distinct species. Following the suggestion of Linnaeus, each 

 species, that is each separate kind of plant, is known to 

 botanists by the name of its genus, followed by a specific 

 name. One particular kind of buttercup is thus termed 

 Ranunculus acris. The classes of plants, with a typical 

 example of each, are as follows : 



I. THALLOPHYTES (no stem], 

 PROTOPHYTA Bacteria. 

 ZYGOSPORE^S Diatoms. 

 OOSPORE^E Fucus. 

 CARPOSPORE^E Most Seaweeds and Fungi. 



II. MUSCINE.E. 



HEPATIC^E Liverworts. 

 Musci Mosses. 



III. VASCULAR CRYPTOGAMS. 



EQUISETINE/E Horsetails. 

 FILICINE^E Ferns. 

 LYCOPODINE/E Club-mosses. 



