14 University of California Publications in Zoology [Vol.22 



the year. Being located almost opposite the Golden Gate, this region 

 is also under almost daily influence of distinct air currents. These are 

 very frequently strong enough to make the water surface quite rough 

 and there is scarcely a day that it is not made ripply for some hours. 

 This also causes important loss of light throughout the year. 



Chemical Conditions Not Studied 



No definite data are available as to the chemical composition of 

 San Joaquin waters. Hence discussion of this important factor must 

 be deferred. 



Tide 



The ocean tide is very much in evidence at Stockton, but the avail- 

 able data are not adapted to satisfactory study. The extreme range 

 is about three feet, but that does not occur very often. The only local 

 records were those from a private tide-guage kept by Dixon Brothers 

 Transportation Company. These records were made very irregularly 

 in connection with the movement of their barges and cannot be used 

 with much confidence in this discussion. 



Aquatic and Marginal Vegetation 



No definite study has been made of the aquatic and marginal vege- 

 tation of this section. The ocasional dredging of all larger water- 

 ways has kept down such growths in the places most accessible locally. 

 Hence the following list must be regarded as incomplete. It is cer- 

 tainly inadequate so far as the typical delta flora is concerned. 



Chara sp. occurs abundantly in some of the ditches and narrow 

 waterways. It has not been observed in the river or in the larger 

 canals, possibly because of the dredging. Where found it furnishes 

 extensive lodgiug places for myriads of microscopic animals and 

 plants. 



Duckweeds, probably Lemna gibba L. and Lemna minor L., are 

 very conspicuous in the fall in quiet nooks and ditches. 



Typha latifolia L. is very abundant in a few places and is fre- 

 quently found in small groups along any water margins. 



AUsma plant ago L. is said to be common. 



Sagittaria is common and three species at least occur in this region. 

 Apparently 8. latifolia Willd is most frequent, though S. greggii J. G. 

 Smith, and S. sanfordii Greene are more characteristic of the locality. 



Urtica holosericea Nutt. is very abundant on most undisturbed 

 levees and water margins. 



