92 BARNARD 



4. Location of the wood sample in relation to tidal changes ; whether 

 it is periodically exposed to drying. 



5. Physicochemical variables of the seawater, such as temperature, 

 salinity, oxygen tension, turbidity, pollutants. 



6. The interaction of the species of wood boring animals present 

 in the area under consideration. 



7. The effects of other animal and plant species, such as the fouling 

 organisms. 



All of these factors enter into the possible appearance and condition 

 of specimens of wood collected in harbors. 



Although several writers have claimed ability to recognize woods 

 infested with Lbnnoria only, distinguishing them from those infested 

 with both Chelura and Limnoria, the writer has often had difficulty in 

 doing this. 



Allman (1847, p. 368) stated that "Timber which has been sub- 

 jected to the ravages of Chelura presents a somewhat different appear- 

 ance from that which has been attacked by Limnoria. ... In the latter 

 we find narrow cylindrical burrows running deep into the interior, while 

 the excavations of Chelura are considerably larger and more oblique in 

 their direction, so that the surface of the timber thus undermined by 

 these destructive animals is rapidly washed away by the action of the 

 sea, and the excavations are exposed in the greater part of their extent, 

 the wood appearing ploughed up, so to speak, rather than burrowed 

 into." 



In harbor areas one may obtain samples of wood which fit All- 

 man's descriptions. In fig. 2A is a sample of wood bored by limnoriids 

 in which the soft layers of the wood have been deeply eroded ; but the 

 hard layers are also riddled with holes and broken off nearly as deeply 

 as the soft layers. The general appearance of the wood is that of a 

 homogeneous accumulation of small subcircular holes ; none of the large 

 caverns typical of chelurid-infested wood is seen. In fig. 2C is a sample 

 of wood infested with both limnoriids and chelurids, which shows the 

 large and irregular caverns associated with chelurid activity and oc- 

 casionally with limnoriid activity alone. This might resemble Allman's 

 description of "ploughed up." 



Several simple laboratory experiments were performed under ideal- 

 ized conditions in order to ascertain differences in wood bored by dif- 

 ferent combinations of animals. Two wooden blocks cut from the same 

 piece of Douglas Fir were placed in separate aquaria and each exposed 

 for four months to an original population of L. tripunctata. At the end 



