66 RHODODENDRONS AT CASTLE KENNEDY 



themselves justice or develop proper luxuriance, and in 

 seasons of exceptional drought many will perish. But 

 it came as a great surprise to those who had given 

 attention to cultivating rhododendrons, when Mr. 

 Wilson, Mr. Forrest, and the late Mr. Farrer announced 

 that in their exploration of Western China many of the 

 finest species which they discovered there were not 

 only growing above a limestone formation, but actually 

 had their roots thrust into crevices of limestone rocks 

 or spread among limestone debris. It must be con- 

 fessed that the earlier reports of these intrepid explorers 

 met with considerable incredulity; but the facts are 

 now established beyond doubt by the testimony of 

 these experienced witnesses, and have opened an 

 avenue which is likely to lead to a notable advance in 

 botanical biology. 



It has been known by botanists for a considerable 

 time that plants of the Heath family, to which rhodo- 

 dendrons belong, depend for the extraction of nitrogen 

 from the soil upon the services of a fungus which 

 envelops and penetrates their roots, creating a inycor- 

 rhiza. It seems probable, though the problem awaits 

 further research, that lime is not directly inimical to 

 rhododendrons, but indirectly so, because it destroys or 

 arrests the functions of the fungus, without which the 

 plant cannot draw nourishment from the soil. Mr. 

 Forrest has discovered that the leaves of rhododendrons 

 growing on limestone have their under-surface coated 

 and penetrated by fungus mycelium, which, forming a 

 mycophyllum, draws free nitrogen from the atmosphere 

 to supply the plant, instead of a mycorrhiza drawing 



