~^T(\ Botanisches Centralblatt. — Beilieft 3. 



portance with the water supplj. The presence of a greater number 

 of succulent forms in these alkaline parts of mesa would indicate 

 this. Certain it is that large quantities of alkali are taken up by 

 plants in these regions. This excessive alkaH in not readily thrown 

 off and the plants must störe the surplus. It is the problem then, 

 not so much to increase capacity for absorption as to decrease 

 the transpiration. Consequently we find that these forms have 

 very small root Systems and a capacity for holding considerable 

 quantities of water. 



As the conditions of light and heat are, as far as could be 

 aseertained, nearly the sarae in all regions, it does not seem pro- 

 bable that they have been iraportant. The prlncipal factor has 

 been water. This has however been determined by a second factor, 

 the soil structure. In the alkaline mesa and in the Strand the 

 chemical nature of the soil has been a factor of equal importance 

 with the water supply. 



As a whole, it will be seen that Orange county is not to be 

 considered as part of the Hartlaubgehölze. In the mountain 

 forraation alone, do we find a pronounced sclerophyll Vegetation. 

 The presence of hairs on both sides of the leaves, the frequent 

 production of spines, the abundance of cactus in foothills, and the 

 tendency toward reduced leaves in mesa formation, all show that 

 we have here a more xerophile region than is usually associated 

 with the Hartlaubgehölze. We may conclude that the main body 

 of the Californian Hartlaubgehölze finds its southern limit sorae 

 distance north of Orange county. The mountain formation represents 

 a tougue of Hartlaubgehölze projecting southward from the main 

 body. The remaining parts of the county are to be considered as 

 a semi-desert, forming an intermediate region between the sclerophyll 

 domain to the northwest and the desert regions to the southeast. 



It is my pleasure to acknowledge the courtesy of Prof. Dr. 

 Engler for the privilege of examining a number of forms from 

 Australian and South African as well as from Californian Hartlaub- 

 gehölze in the Berlin Museum. 



Bibliograph y. 



1876—80. Brewer, W. H., Watson, S. and Gray, A., The botany of 

 California. 



1895. Hook er, J. D, and Jackson, B. D, Index Kewensis. 

 1890. Drude, O., Handbuch der Pflanzengeographie. 



1896. Warming, E., Lehrbuch der ökologischen Pflanzengeographie. 



Deutsch von Knoblauch. 

 1898. Schimper, A. F. W., Pflanzengeographie auf physiologischer 

 Grundlage. 



