(3i) 



as a group perhaps attract the attention of a greater number 

 of people than any other group of plants. However, associ- 

 ated with what are usually known as ferns are the fern-allies, 

 for example the ''horse-tails" {Equisetum), " lycopods " 

 CLycopo'dmm) and ' ' quill worts " (Isoetes), but these are usually 

 less conspicuous than the "ferns." Fern-plants differ from 

 all the plants of simpler organization in having vascular 

 (woody) tissue, that is, a system of vessels for conducting sap 

 through the different parts of the plant-body. They exhibit 

 an almost infinite variety of form ; their stems may be under- 

 ground, horizontal on the ground, or erect; the leaves are 

 either simple or compound, and sometimes perform both the 

 work of foliage leaves and that of bearing the spore-cases 

 (ferns), while in other cases some of the leaves have become 

 changed into mere spore-bearing organs (horse-tails). 



The flowering plants (cases 56 to 128) comprise a single 

 subkingdom, the Spermatophyta or seed-bearing plants. 

 This extensive group seems to have followed two independ- 

 ent lines of development and consequently the plants fall into 

 two well marked groups, the first being the gymnosperms, 

 cone-bearing plants, or plants in which the seeds are borne 

 exposed in variously shaped cones (cases 56 to 58). This is a 

 comparatively small group, but exhibits great diversity, in- 

 cluding plants ranging from straggling shrubs or vines to the 

 largest trees. The leaves, too, vary from structures resem- 

 bling needles or scales to expanded fern-like structures of 

 considerable variety. In a former geological age these 

 plants were the dominant seed-bearing plants, but now the 

 second group of the spermatophytes largely predominates ; 

 namely, the angiosperms, fruit-bearing plants, or plants in 

 which the seed is borne in a seed-case. These plants also 

 existed in the later geological ages, and now form the most 

 important and conspicuous part of the vegetation of the earth. 

 The fruit-bearing plants (cases 59 to 128) fall into two divis- 

 ions, the one in which the seed contains a single leaf, the 

 monocotyledons (case 59 to 71) ; the other in which the seed 

 contains two leaves, the dicotyledons (cases 72 to 128). 



