28 I'l.ANT I.IFK «»K A I. A HA MA. 



to tlii'ir suiTouiiilinus with tM|ii:il finilily. llit'ir would lit- no limit to 

 tlu'ir tlispcrsioii o\irr\(M\ j):irt ot the ;^lol)r wIhtc lite exists, only 

 witii tlu' i-('st'i-v:itioii that in thr st rii»:«rlf for the possession of the 

 tji-oimd tho>c of JiJLihesI \ itality. endowed w ith ti'i'i'iitest power of re- 

 production and possessed of spei'ial facilities for dissemination, would 

 overcome the less faxored and e\-entually establish themsel\-es, to the 

 exclusion of others, upon the a\ailal)le space. It is by the di\ersity (d" 

 theii- ( limatic recpiirements. their \iiryiii«z' decrees of dependence upon 

 the uni\ersal en\ ironmental factor.s — air. liuht. heat, and moisture (the 

 last two heinu- tl"' principal ones)--tliat jdaiits are restri<'ted within 

 specitic limits. 



The dependence of plant distribution upon heat is demonstrated l)y 

 the ditl'erent character of the vegetation under ditiorent parallels from 

 the poles to the ('(piator. and vertically in the ascent from the shore of 

 the sea to the heiiihtsof the mountains. As Alexander von Humboldt 

 oraphically and ehxiuently expresses it: '* I'nlike in design and weave 

 is the '-arpet whicii the plant world in the abundance of its flowers has 

 spread over the naked crust of the earth, more denscdy woven where 

 the sun ascends hioher on the cloudless sky, looser toward the slug- 

 gish poles, where the early returning frost nips the undeveloped bud 

 and snatclu's the barely matured fruit. Kvery zone is endo^ved with 

 peculiar charms — the tropical in the variety and grand development of 

 its production, the northern in its fresh meadows and in the periodical 

 revival of nature and the influences of the first breezes of the spring. 

 Besides having its own special advantages, every zone is marked by a 

 peculiar character." It is a fact well established by observation that 

 the same or more or less closely related ft)rms will often appear under 

 similar climatic conditions in parts of the globe widely separated by 

 oceans or deserts. This applies, if not to predominating specitic and 

 generic types, at least to representative orders. On the summits of 

 mountains, covered for the greater part of the year with snow and ice, 

 plants are found which are at home in the Boreal Zone; again, the flora 

 of the equatorial zone bears the same gejuM'al features around the globe. 

 Plants with the same climatic recpiirements, calling therefore for the 

 same physiological fimctions, nin-essarily show similarities in their 

 morphological development, and thus we fljid that in difl'erent parts 

 of the globe the plants exhibit a stronger or feebler resemblance 

 morphologically. 



PLANT ZONES OF HUMBOLDT BASED ON ISOTHERMAL LINES. 



Alexander von IIuml)oldt was the flrst to divide upon these princi- 

 ples the surface of the globe into botanical zones and to lay the foun- 

 dation of the science of plant geograpliy . Each of these distinct zones 

 of plant life exhibits features which are al)sent or at most more or less 

 feebly represent(Hl in the other zones. 



