221 



its molhor plr.iit Avas sickly and its <)^raiidinotlier would havo died at 

 oneo. It was iii recognition of this view that in the eiji:hteenth cen- 

 tury the hotanical warden at Teneriffe was established (the so-calleil 

 acclimatization <i:arden at Durasno and the Colegan (larden at Oro- 

 tava, at an altitude of 1,040 feet) in order to furnish a temporary 

 resting place for tropical plants that they mii?ht accustom them- 

 selves to a cooler climate preparatory to their cultivation in southern 

 Europe. According- to Dollen, the same principle is applied in the 

 acclimatization garden at Algiers to tropical African i)lants before 

 their transportation into southern France. 



. As the guiding thought of his second memoir, Linsser now remarks 

 that we must divide the vegetable phenomena- of the world into two 

 divisions, viz, those in which temperature controls the annually re- 

 curring cycle of phases, as is the case in the Temperate Zone, and thosi^ 

 in Avhich moisture controls, as in the Tropical Zone. Thus, on the 

 grassy plains of South America, where the year is divided into a dry 

 and a wet season, the entire course of vegetation depends upon the 

 latter; the hottest and driest season exerts upon the vegetable life an 

 influence like that of the northern winter, bringing, namely, rest and 

 even death. Such a contrast is even found at Madeira, where, accord- 

 ing to Heer, the weeds of northern P]urope begin to vegetate in the fall 

 after the dry summer months of trade winds and when the first rains 

 fall, whereas in the hottest summer time all these Aveeds slumber or 

 die, as with us in winter. Tn the steppes of Orenburg, Russia, when 

 the sun melts the snow in April, it starts the first sprouts and the 

 blossoms, and by the beginning of May the vegetation of the steppes 

 has attained its highest brilliancy, being distinguished by the great 

 number of many-colored tulips, as has been so often described by 

 travelers; but this beauty passes b}^ with remarkable rapidity, and 

 when in June the dry, hot summer of the steppes begins, all the \cr- 

 dure is dry and dead, and in place of the blossoms there are seen only 

 the dry, empty hulls; so that the wdiole life of the plants on the 

 steppes is condensed into the short space of eight weeks. 



We thus see that for large portions of the earth the heat as such 

 ceases to be the principal regulator of plant life, and moisture becomes 

 the controlling influence. 



It is evident that the life of plants depends upon both temperature 

 and moisture. In situations where there is always sufficient moisture 

 the influence that decides whether or not a plant shall develop is the 

 heat; but in regions Avliere there is always sufficient heat that deciding- 

 influence is moisture. Therefore Linsser proposes in his second me- 

 moir to first state the influence of heat on vegetable phenomena more 

 precisely than he had previously done, and then to develop the influ- 

 ence of moisture. 



