128 ANNIVERSARY ADDRESS 



excess may not produce indigestion ? Some hermit- 

 crabs carry about sea-anemones on the shells they inhabit, 

 and this not accidentally, but of set purpose. In one 

 case the anemone always fixes itself under the mouth 

 of the shell. This would seem to be a partnership, for 

 we are told that the anemone is useful to the crab as 

 a mask, and as the equivalent to a stinging organ, and 

 in return the anemone is carried about by the crab on 

 various " Naturalist " excursions, and also receives " the 

 crumbs that fall from the rich man's table," that is, from 

 the mouth of the predominant partner, the crab. It is 

 certainly curious that the Commensalism here alluded to 

 should find its close counterpart in the vegetable world. 

 Professor Boulger, F.L.S., F.G.S., under the title of 

 " Co-operative housekeeping among plants," deals with 

 " Symbiosis," or living together, and states that while 

 the term was intended to stand for mutual benefit, it 

 was thought better that it should include three expres- 

 sions ; 1st, Mutualists ; 2nd, Commensuralists ; and 3rd, 

 Parasites.* The orchid is symbiotic, but only as a 

 Mutualist, for it is merely resting on the tree, not 

 nourished by it. The lichen is a degree higher, for it 

 is generally permitted to sit at the same table with 

 its host, and hence called a Commensuralist. The 

 mistletoe represents the Parasites. In a lecture by Rev. 

 Professor Henslow we were informed as to mutuality 

 under a different phase, i.e. where this peculiarity is 

 manifested in the same single plant. Almost any part 

 or organ can, if required, take on the functions of some 

 other organ, with or without undergoing much alteration 

 of structure. " This," he adds, " is what I have called 

 Mutual accommodation among plant organs." " The Study 

 of Homology and Analogy" was an alternative title of 

 the lecture, and, for illustration, reference was made to 



* Trees half Alder half Mountain Ash, Dr Hardy, Vol. vi., p. 365 

 (1872). Elder on Apple tree, Capt. Norman, Vol. xvii., p. 1-15 (1899). 



