NORTHERN ZONE OF HOT SUMMERS 187 
shore is muddy, as in estuaries, a somewhat different flora 
appears. Farthest out occur masses of Zostera, then 
Salicornia herbacecr, both are entirely submerged at high 
water. Further inland, out of reach of most tides, where 
the ground is firmer, occur Glyceria maritima , Triglochin 
maritimum , Plantago maritima , Suaeda maritima , Glaux, 
Statice, Cochlearia, Spergularia marina , Aster tripolium , &c. 
Higher up still many of these disappear, their places being 
taken by Armeria, Festuca, Erythrea, Juncus sp., &c. 
Many shore plants in Europe are also found on moun- 
tains, a fact easily understood after a comparison of the 
general conditions of life. Thus in Britain, Armeria, 
Plantago maritima , Silene maritima , Cochlearia maritima , 
&c., occur on the mountains at high levels as well as at the 
coast, but are rare or unknown in the intermediate districts, 
and in the same way, on the west coast of Scotland some 
alpine forms, e.g. Saxifraga oppositifolia, occur at the sea-side. 
In the more southern parts of this zone rain is rare in 
summer, and the transition to the following zone is gradual. 
III. Northern zone of hot summers 1 . This 
comprises the subtropical regions lying between zones II. 
and IV., i.e. the basin of the Mediterranean (including 
Spain and Italy), Asia south of zone II. (excepting India, 
Indo-China, the Malay Archipelago, and the S.E. coast 
of Arabia), North Africa, the Sahara, and the rest of the 
United States and Mexico. The summer temperatures 
are very high, higher than in the tropics; at night it is 
often cold. There is no real winter, but at most a slight 
interruption of vegetation in January. The rainfall varies 
considerably, and whilst the zone includes the driest parts 
of the world, it also contains, in Florida, parts of Mexico, 
South Japan, &c. comparatively wet regions, characterised 
by dense forests not unlike those of the wet tropics, but less 
rich in climbers and epiphytes, though in Tillandsia usneoides 
the forests of the southern United States possess probably 
the most dominant and striking of all epiphytes. In the 
Mediterranean and Californian regions the rainy season is 
in the winter, and there is less development of forest. 
1 Schimper, etc., op. cit.\ cf Xerophytes, etc., above; Berger in 
Bot. Gaz. xxxv, 1903, p. 350 (Macchie) ; Burtt Davy in Bull. Bureau 
Plant Ind. U.S. Dept. Agr., Washington, 1902 (California). 
