178 MORPHOLOGY OF SPERM ATOPHYTBS 



and by the occasional remarkable exceptions. Six apparently 

 natural groups are recognized, and each one belongs distinctly 

 to the northern or southern hemispheres. Taxeae, Abieteae, 

 Taxodieae, and Cupresseae are distinctly northern types; while 

 Podoearpeae and Araucarieae are just as distinctly southern. 

 It is interesting to note that this division disregards the great 

 division of Conifers into Taxaceae and Pinaceae. 



While this is the general fact, it is more or less true in the 

 different groups. For example, Abieteae are absolutely north- 

 ern and Araucarieae are absolutely southern, but the same 

 sweeping statement can not be made in reference to the other 

 groups. Podoearpeae, characteristically southern, are repre- 

 sented in eastern Asia by species of Podocarpus. The three re- 

 maining northern groups, however, show more striking depart- 

 ures from the rule. Taxeae are represented in the Australasian 

 region by the endemic genus Pliyllocladus; Taxodieae are rep- 

 resented in the same region by the endemic genus Arthrotaxis ; 

 while Cupresseae are represented in the southern hemisphere by 

 the endemic Australasian genus Adinostrobus, the Australasia- 

 African genus Calliiris, and the Australasia-South American 

 genus Fitzroya. The occurrence of these widely separated gen- 

 era, on the hypothesis that they belong to the same natural 

 group, is an interesting problem. 



From the standpoint of isolated genera, however, the Tax- 

 odieae are most interesting, for all of the seven genera are very 

 much restricted. Glypiostrobus is Chinese, Sciadopitys is 

 Japanese, Cunninghamia and Cryptomeria are China-Japanese, 

 Arthrotaxis is Australasian, Sequoia is Californian, and Tax- 

 odium is east North American. 



The facts presented above can be understood only when con- 

 nected with the ancient distribution of the various groups, but 

 unfortunately the history of Conifers is not in a condition to 

 supply definite testimony. 



GNETALES 



Ephedra (30 spp.) occurs in the arid regions of Mediter- 

 ranean Europe and adjacent Asia, as well as of America, in 

 tropical, subtropical, and temperate conditions. Gnetum (15 

 spp.) ranges through the tropics of both hemispheres. The 



