492 MANUAL OF NATURAL HISTORY. 



cotyledons, and their stems are Exogenous, but they 

 are distinguished by the vessels of the wood having 

 large apparent perforations. Their chief peculiarity, 

 however, consists in the naked, uncovered condition 

 of the seed, and in the fertilization of their female 

 organs taking place through the foramen of the 

 ovule, without the aid of either style or stigma. In 

 general appearance they bear a strong resemblance 

 to some flowerless groups, as the Club-mosses and 

 Ferns, so much so as to have been, by Linnaeus and 

 others, classed with the latter. They contain the 

 curious Joint-Firs, the melancholy Yews, the in- 

 valuable Pines, and the feathery Cycads, comprising 

 in all, thirty-seven genera, and upwards of two 

 hundred species. 



II. CLASS.— GYMNOGENS (Gymnogense). 



A cellular and a vascular system ; stem with 

 wood and true bark ; vessels of wood with large 

 apparent perforations ; wood in concentric zones, 

 augmented by growth from without ; embryo di- 

 cotyledonous ; ovules fertilized by direct contact, 

 without the intervention of style or stigma; ger- 

 mination exorhizal. 



1. Family. — Joint-Firs (Gnetacese). Small trees 

 very much branched, or sarmentose shrubs; 

 juice watery; stems jointed; leaves opposite, 

 simple, net-veined; flowers in catkins or 

 heads; male flowers with a perianth ; female 

 flowers naked, or sheltered by a false peri- 

 anth ; anthers 1-4-celled, opening by pores ; 



