278 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



Mese?nbryanthemum colonies. One of the most successful of the 

 plant invaders of the south-western islands is Mesembryanthemum 

 crystallinum. It has colonized large areas on San Clemente, San Nicholas, 

 and Santa Barbara Islands. In these colonies it monopolizes the ground 

 surface so that only a few other plants can become established. Such 

 colonies occur on the east and west flanks of the north peak, the east 

 flank of the south peak, and near the north and south ends of the eastern 

 terrace. Only a few plants of Hordeum murinum, Chenopodium murale, 

 or Suaeda californica pubescens seem able to maintain a foothold in 

 these colonies. If they survive the competition they grow luxuriantly and 

 Hordeum will remain green for weeks longer along the margin of a 

 Mesembryanthemum colony than elsewhere. One of the most remarkable 

 features of the pure stands is that they appear to occupy exactly the 

 same areas for years. Thus the large colony on the east side of the south 

 peak had been seen from Santa Catalina by the writer, with the aid 

 of field glasses, fifteen years earlier, occupying the same area it does 

 today. 



Suffrutescent cotumunities. The greater part of the western terraces 

 appears to have been free from such extensive burning and cultivation 

 as the upper part of the western terrace. Low native suffrutescent shrubs 

 and herbs occupy most of the area. While Hordeum is abundant in 

 most of the openings it holds a distinctly subordinate position. Suaeda 

 californica pubescens is a dominant in the upper portion of the main 

 terrace at the foot of the main ridge and in a cross-drainage depression 

 that opens toward the northwest. Mesembryanthemum crystallinum and 

 M. nodiflorum are present in small or medium sized colonies among the 

 Suaeda. 



Edaphic and climatic conditions are very similar to those on the 

 east terrace. The surface soil is fine, containing 39.19 per cent silt and 

 clay, and there is an exceptionally large amount of colloidal material 

 present, possibly due to the droppings of the gulls which nest here. 



Lyciu?n calif ornicum is dominant throughout the middle and western 

 end of the main western terrace, where the elevation is a little higher, 

 the soil somewhat shallower and of coarser texture, and the wind veloc- 

 ity somewhat greater. Galium aparine occurs closely associated with the 

 Lycium, and Achillea millefolium lanulosa occurs in isolated clumps, 

 where the habit of the plant closely resembles that of the variety mari- 

 tima which has been previously reported only from the San Francisco 

 Bay region. Brodiaea capitata is also found on the southwestern slopes 

 of the terrace. 



