524 A TEXTBOOK OF BOTANY [Cn. XIII 



Ecologically the Coniferae are all terrestrial plants, with 

 a partly xerophytic habit. Phylogenetically they have an 

 ancient lineage of their own, without any direct relations to 

 the Cycads; for apparently they are derived from the ex- 

 tinct group of Cordaitales, which early diverged from the 

 Cycadofilicales (Fig. 275). 



ORDER 3. GNETALES : THE GNETUMS AND KIN. A small 

 group, only some 50 species, but interesting because in- 

 cluding the most highly specialized of the Gymnosperms, 

 Here belongs the remarkable Welwitschia, or Tumboa, of 

 Southwest Africa (Fig. 42), Ephedra, 

 mostly leafless shrubs of dry regions 

 somewhat resembling much-branched 

 Equisetums, and Gnetum, which in- 

 cludes tropical trees and vines. Their 

 wood has ducts in the secondary 



FIG. wo'wdwtachia g rowth as in Angiosperms, and, what 



mirabiiis, showing abortive is more remarkable, they possess a 



fiTr^V"'": sort of ovary surrounding each ovule, 



(From Le Maout and - composed, however, 'not of sporo- 



phylls, but of a special integument 



which is prolonged into a flaring tube simulating the ovary, 

 style, and stigma of the Angiosperms (Fig. 370), though 

 there is probably not the least relationship between these 

 groups. The flowers of Gnetacese, alone among Gymno- 

 sperms, are apparently pollinated by insects. The group 

 has certain relations with Cycads, ultimately through the 

 Cycadofilicales. 



CLASS 2. ANGIOSPERMS : THE ANGIOSPERMS 



These comprise the plants with true flowers in the popular 

 sense, and thus embrace the great majority of the familiar 

 and favorite kinds. Some 133,000 or more species are known, 

 which is more than half of the total number ; and they in- 

 clude most of the kinds which are useful, especially as food. 



