540 



BOTANY 



PART II 



Corsican Pine from Austria ; P. Pinaster, Maritime Pine from tlie Mediterranean 

 region ; P. taeda, P. Strohus, "Weymouth Pine, P. Lamhcrtiana from N. America. 



Cedrus. — Cedars from the forests on Atlas and Lebanon. Cultivated. 



Poisonous. — Juni^icrus Sahina, Taxus haccata. 



Official. — Pinus sylvestris and other species produce oleum terebinthinae 

 and KESINA ; Abies halsaviea supplies terebinthina cakadeksis ; P. jxdustris and 

 P. taeda yield thus americanum ; P. excelsa yields fix burgundica ; P. sylvestris, 

 etc., nx LIQUIDA ; P. pumilio, oleum pini ; Juniperus oxycedrus and other species 

 yield oleum cadinum ; Jiini2)ervs communis, oleum juniperi. 



Opder 4. Gnetinae (-*^) 



The only Family in this order is that of the Gnetaeeae, to which 



only three genera belong : JEj^hedra (Fig. 511), leafless shnibs of warm 



dry regions of the northern hemisphere ; 

 IFelwitschia mirabilis, a monotypic plant 

 from the deserts of South-West Africa ; 

 the widely expanded summit of the stem 

 bears after the cotyledons only a single 

 pair of leaves, which are 1 m. in length 

 and continue to grow at their bases ; 

 Gnetum (Fig. 51 2), tropical trees or climbers 

 with pairs of broad, reticulately veined 

 leaves. These genera, while differing 

 widely in appearance, agree in possessing 

 opposite leaves (in Ephedra reduced to 

 scales), in the development of vessels in 

 the secondaiy wood, the absence of resin 

 canals, and in the presence of a perianth 

 to the flowers which are usually dioecious 

 (Fig. 513). 



These points of agreement Avith both 



Ym.bn.-Ephedraaitissima. i, Habit Gymnospemis and Angiosperms make the 

 of a male inflorescence. 2, An group in many ways an intermediate one 



between the two classes. Insects visit 

 the flowers of TVelwifschia and Gnetum. 



The development of the sexual generation (cf. p. 509) in the three 



genera is as various as their external habit. 



inflorescence with nnripe fruits. 

 (§ nat. size.) 



Fossil Gymnosperms (-i) 



In contrast to what was seen to be the case for the Pteridophyta, Gymnosiierms 

 have not yet been detected in Cambrian and Silurian strata. They appear first in 

 the Devonian, but are sparingly rejiresented and first form an important constituent 

 of the flora in the Carboniferous. From the Cycadofilices, which possessed stems 

 with secondary thickening and fern-like foliage and had been hitherto regarded as 

 Pteridophyta, Oliver and Scott (2''') have recently separated the Pteridospermeae ; 



