335 



the shore of Bay Farm Island. Alanieda. Wood apparently pla\s the role of a second- 

 ary habitat, or the organism might be regarded as in a transitional stage of adaptation 

 to a wood-boring lite. 



Sound Douglas fir piling is rareh' attacked unless it be unusually soft and open 

 grained. I^ut the surface of piling that has been attacked and partly destroyed by 

 Teredo is often secondariK- attacked by Sphacrnma, which finds boring an easy matter 

 in the already honeycombed wood. Most of the evidences of the work of Sphaeroma 

 that w-e have seen have been in piling of this sort. The boring of this organism is 

 apparently for the purpose of securing shelter only, and it accordingly imbeds itself 

 in the first suitable substance with which it comes in contact, Ije that substance stiff 

 clay, soft rock, or piling, the surface of which is already broken down by the activities 

 of Teredo. 



Fig. 139. Pile at China Camp, on the- west shore of San Pablo Bay, attacked by Sphaeroma pentodon 

 between tide levels. 



Some instances have been observed, however, of damage to piling occasioned by 

 this borer alone, in the absence of attack by Teredo. This has usually occurred in 

 old piling that has been subjected to alternate wetting and drying between tides for 

 many years, and its surface affected to such an extent that Sphaeroma easily finds 

 lodgement in it. Such a case is that shown in figure 139. Much of the piling in which 

 we have observed attack by Sphaeroma alone has been standing so long that the tops 

 have been practically destroyed by dry rot, so that the damage occasioned by the 

 borers is of little consequence. 



The test board shown in figure 138 was exposed for three years at the Petaluma 



