Chapter X — 189 — Historical Causes 



fourth genus, Microcycas, very closely related to Zamia, is now confined 

 to Cuba. Another group of Zamiaceae spread southward from the 

 equator of the Permian period into Africa, where, as the climate gradu- 

 ally became warmer, it reached, by way of eastern Africa, the Cape of 

 Good Hope. Of this group there has been preserved the genus En- 

 cephalarlos. From eastern Africa closely related forms spread, by way of 

 Madagascar and the East Indies, to Australia, which lands at that 

 time formed with Africa a vast, united land-mass (Gondwanaland) . 

 In east Australia (New South Wales) we find the genus Macrozamia, 

 which is closely related to the African Encephalartos and the American 

 Zamia. 



The group of Cycadaceae proper, represented by the genus Cycas, 

 is probably also of African origin. Although in Africa itself it has 

 not been preserved, we find its most ancient representative, Cycas 

 Thouarsii, on Madagascar and the Comoro Islands and a very close 

 relative of this species, Cycas circinalis, in the East Indies. From these 

 regions this group is presumed to have spread to adjoining Australia. 

 Lastly, the East-Asiatic forms {Cycas siamensis and C. revoluta) reached 

 their present habitats by way of the East Indies. 



Schuster (1931) holds a different view. In his opinion the initial 

 forms of the family Cycadaceae arose on the Eurasian continent. These 

 Upper Triassic cycads [Ur-Cycadaceae) gave off two branches that 

 spread from the ancient continent of Angara, one to Gondwanaland 

 and one to North America. From the Tertiary descendants of these 

 initial forms there arose our present-day cycads in different centers, 

 such as the Himalayas, western Australia, South Africa, Mexico, and 

 Central America. This investigator considers that his data controvert 

 Wegener's theory, but, in order to explain them, he has to assume 

 that there existed continents where now there is sea, which is refuted 

 by modern geology. 



Ginkgoales. — The distribution of the Ginkgoales — represented in our 

 present-day flora by only one relic species, Ginkgo biloba, growing in 

 Japan in forest reserves and possibly wild in China — has been studied 

 by Shaparenko (1935, 1936) with the special aim of testing Wegener's 

 theory. Ginkgo in past geological periods had a very extensive area in 

 the northern hemisphere, as shown by the location of its fossil re- 

 mains, known as Ginkgo adiantoides. Moreover, changes in the location 

 of the area of Ginkgo in different geological periods coincide with 

 remarkable exactitude with changes in the location of the 40th parallel 

 as given by Koppen and Wegener (1924): — 



"The most ancient finds of this species — Ajakit [Siberia], Cape Boheman [Spits- 

 bergen] — are located in the tertiary of Angarida, seemingly the center of the growth of 

 this species. According to Wegener, this region should have lain at about 40° north 

 latitude, which almost coincides with the latitude of the area of the Uving species now 

 growing in a half-wild state" (Shaparenko, 1935, pp. 15-16). 



In Cretaceous deposits Gingko is again found in the Far East, but it 

 is also found in Greenland and in North America (Upper Cretaceous). 

 In intermediate localities it has not yet been found. These fossil 

 occurrences lend support to the presumption that these territories were 

 at that time connected, since they cannot be explained by chance 

 transport of seeds. The seeds of Ginkgo, as those of other gymno- 



