F. T. Brooks and A. Sharples <>•"> 



a number of small vessels included in a larger one. In the majority 

 of cases only the thin-walled type occurs. Their contents are devoid 

 of food reserves. 



The response made by living cells to an injury usually results in 

 an abnormal growth of neighbouring cells. In Hevea brasiliensis 

 attacked by Pink Disease an abnormal bladder-like ingrowth of the 



Fig. 3. Longitudinal section showing hyphae passing from medullary rays into vessels. 

 Hyphae pass through without constriction. (Drawing somewhat diagrammatic.) 

 xl60. 



living cells bordering the longitudinal path of the fungus, i.e. the 

 vessels, takes place. 



The formation of tyloses as a traumatic response is presumably an 

 attempt on the part of the host to check the passage of the fungus 

 through the tissues. In this case it is obviously unsuccessful as the 

 hyphae easily pass through the tyloses (Fig. 4). Failing this function, 



Ann. Biol, n 5 



