ZONAL DISTRIBUTION. 



.1 



seen in the South Indian species already discussed, winch both have alternate leaves, 



although in the Himalaya itself there are no m as many opposite-leaved M there are 

 alternate-leaved forms. 



Although the distribution of the genus is almost entirely meridional, examples of the 

 distribution of the same species along several meridians are not very common. Besides 

 that of P. verticillata, the most striking instances are those of P. Oederi and P. Sccptrum, 

 which both occur within the Circumpolar province and both extend along the European 

 and the Siberian meridians. P. Oederi extends along the Chinese meridian also as far 

 as the Himalaya, but in a somewhat different condition (var. hcteroglossa). P. Seeptrum, 

 on the other hand, is represented in Japan only by a closely alli< I, but perfectly 

 distinct, species (P. gloriosa). P. sudetica also occurs in the European and Siberian 

 meridians, but is altogether absent from the Himalo-Chineso. On the other hand, it is 

 represented in the American meridian by the closely allied, although perfectly distinct, 

 P. scnpulorum. 



Nor are the species that have become part of the Intermediate Flora, and that are 

 thus characterised by a zonal distribution, very numerous. In the Temperate Zone, as it 

 is usually understood, the most striking examples are P. palustris, euphrasioides \ tylvatica, 

 and resupinata. P. palustris extends from the British isles throughout Europe, Siberia, 

 Kamtschatka, Alaska, and Rupert's Land to Canada, — throughout the entire temperate 

 complement of the Circumpolar province in fact. P. sylvaiica extends from the British 

 islands across Europe only ; its extension to South-Eastern Scandinavia is, as Mr. Ulytt 

 has shewn, an instance of comparatively recent immigration. 1 P. rempinata extends 

 across the whole of Siberia and North China to Japan. P. euphrasioides extends from 

 Kamtschatka through Alaska, Rupert's Land, and Labrador to South Greenland. It is 

 thus a sub-arctic species rather than a truly temperate one. The comparatively recent 

 occupation of their temperate habitat by these species is evidenced by the fact that 

 they pass from the Japanese to the American meridian uninfluenced by the ancient 

 cleavage that the truly Arctic flora indicate-; as separating these. 



Species with this zonal type of distribution are not, however, confined to the 

 temnerate complement of the Circumpolar province. The few species that descend to 

 comparatively low elevations in the Himalaya exhibit the same phenomenon. Thus 

 P. carnosa extends at elevations of 5,000-7,000 feet from Kashmir to Khasia, P. rex 

 at similar elevations from Khasia to Kwei-tschou. The parallelism between these and 

 P. sylvatica and P. resupinaU respectively is complete. Nor is this all; for just as we 

 have seen that P. palustris occupies the fringe of the Circumpolar province 

 extent, we find P. gracilis at elevations of 6,000-10,000 feet in every Himalayan 



district from Afghanistan to Yunnan. 



There are no species in the temperate complement of the present European Alpine 

 province with a zonal distribution like this. And the absence of any such phenomenon 

 there corroborates very strikingly the evidence concerning the tract derived from other 

 sources. We have already supposed that an ancient Mediterranean Ocean prevented an 

 ^,sion beyond their present limits of the European and Sibeno-Caucasus meridians. 

 Mr Ball 2 and Mr. Dyer * have independently arrived at the conclusion that the shores 



in its 



exten 



^ . .■ r*i* TV n *n?aian Flora during alternating rainy and dry period*, p. 7» 

 1 Axel Blytt : Essay on the Immigration of the Norwegian riora y 



' Ball : Spicilegium Flora Maroccana; Jour. Linn. Soc. xvi, 3 ft, 



3 Dyer: Plant Distribution e$ a field for Geographical Research, p. 10. 



Ann. Rot. Bot. (jard. Calcutta, Vol. Ill 



