McKenney, Notes on Plant Distribution in Southern California. 175- 



magnitude. Rather it is the relation of that Factor to other factors. 

 that is important, that is, it is the relative magnitude. 



If we examine the conditions in Orange County, we find that 

 most of the factors are nearly alike in all parts. Two factors vary, 

 the water supply and the ground. As Schimper has shown, it 

 is not the amount of rainfall that alone determines plant growth 

 It is the supply of water which can be tapped by the roots. This 

 supply is dependent on a number of things, among others on the 

 structure and Constitution of the substratum. 



It will readily be seen, that although the sarae amount of 

 rain falls in all parts, still the amount of water in soll of the 

 different formations must vary. The caüons, receiving the drainage 

 from the foothills and mountains, naturally have the largest water- 

 supply in the soil. Accordingly it is here that we find the nearest 

 approach to a mesophytic type of Vegetation. The mountains» 

 having a larger surface and bulk, absorb and hold much more 

 water than the foothills. The lewer part of the mountain also 

 receives drainage from the upper part. The tiny Springs, which 

 are only present on the mountains, would also indicate that they 

 have a larger amount of soil water than the foothills. 



This difference in water content of the soil, readily explains 

 the difi^erence between mountain and foothill formations. With less 

 soil water, when in both cases the amount in not large, it is evident 

 that the hills could not suppart the same amount of shrub growth 

 in a given area as could the mountains. The larger number of 

 shrubs in mountains would also prevent a spreading habit. The 

 open areas among the foothill scrub, afford opportunity for growth 

 of forms not requiring so much water, namely herbs. The succession, 

 ot herbs in the foothill constitutes a good indicator of the amount 

 of soil water. The earlier forms are greener, and are less hairy 

 than later forms, As the season advances, we find the cuticle 

 becoming thicker and the hair covering more extensive. In the 

 driest period, herbaceous growth in the foothills is very scanty. 

 The abundant cactoid growth is another indicator of the smaller 

 water supply in the foothills. 



The raesa, which receives but little drainage from other regions, 

 is dependent very largely on the rainfall for its water supply. 

 The conditions here — no shade, dry atmosphere, and uninterrupted 

 wind sweep — all tend to promote a rapid transpiration. Consequently,. 

 in the way of hardness and spininess of parts, we find muc'i re- 

 semblance to a desert flora. 



The River Bed formation owes its characters to the water 

 flow in the wet season. The water smothers most herbaceous growth 

 white furnishing araple water for the shrubs. In the Dry season, 

 the river beds are subjected to the same conditions as the mesa, 

 with exception that the moisture containing soil layers are nearer the 

 surface in the river beds; although deep enough to be out of 

 reach of roots of most herbs. 



In the more alkaline section of the mesa and in the Strand, 

 doubtless the chemical nature of the soil, has been of equal im- 



