nicii^ of tin's L;rass. for il is likcK' lo be Ih a^nirilis N'asey, an- 

 I'tluT i)l;int wliirli was tirsl found 1)_\' ( )rcutl in the v'^an Dic^o 



|)( )o!s. 



I\c(l llill oiTcr.s on a small scale a very clear example of the 

 ecological limitation of plant growths. The vegetation of the 

 mesa is composed of the native and naturalized ]:)lants common 

 everywhere in the region in similar places. Not one of them had 

 intruded on the pools, from which they are excluded by the pres- 

 ence of water at the time when their seeds sprout. It would be 

 interesting to observe if they are able to enter in those very dry 

 seasons when the deficient rainfall fails to fill the pools. Of course 

 none of the ]:)lants of the pools are able to ]Dass beyond their 

 narrow limits. With tw^o exceptions they are among the least 

 known plants of Southern California. The exceptions are Psilo- 

 carphns glohifcnts and Navarrctia prostrata, which appear to be 

 not uncommon in desiccated pools in the coastal district of Los 

 Angeles county. But neither the commoner nor the rarer species 

 have been found elsewdiere at any but places remote from this 

 station. Botanists who are acquainted with the location of such 

 winter pools should examine them with care early in the rainy 

 season to ascertain if the rarer plants are not to be found in 

 them. After the more conspicuous plants are in condition for 

 collecting the smaller ones wall probably have entirely disap- 

 peared. 



52 



