THE GENUS EPIPACTIS IN BRITAIN 213 



Fig. 21. (Cardigan.) Here the b(3sses are very elevated and clear- 

 cut, and the narrow central boss is clearly marked out from the others. 



Fig. 22. (Cardigan.) Smooth side-bosses and a shallow tri- 

 angular central elevation with a small boss upon it. 



Fig. 23. (Owl Wood, Surrey.) No centre boss. Side-bosses fairly 

 rugged. Leaves broad. 



Fig. 25. (Cardigan.) Fairly wrinkled side-bosses and slight 

 central elevation. Leaves very broad. 



JPigs. 24 and 26. Reproductive organs. 



Fig. 2-1 shows the organs of E. lafifolia, and Fig. 26 those of 

 E. viridijlora v. leptochila. The difference between the slender 

 organs of viridiflora with receding stigma, friable pollen-masses, and 

 rostellum so small as to be barely visible ; and the stouter organs of 

 latifolia with stigma pushed well forward, more coherent pollen- 

 masses, and large rostellum, is well brought out. 



It will be clear from a study of the lips of E. latifolia shown 

 above how very much and in what elusive ways these lips vary as far 

 as most of their details are concerned. The grades of variation, 

 indeed, are so difficult to separate that hardly any two people will 

 quite agree as to the exact words which should be used to describe any 

 given lip. We hope that the figures will illustrate our case where 

 verbal description is at fault. 



Errata in paper on Orchis purpiirella in July issue : — 

 p. 167, line 23 : for " 35 cm." read " 15 cm." 

 p. 169, line 18 : for *' leaf -pattern " read " lip-pattern." 



THE LICHEN SYMBIOSIS. 

 By a. H. Church. 



" Lichens are symhiotic organisms^ they consist of higher Fungi, 

 chiefly Ascomycetes, more rarely . Basidiomycetes, and unicellular 

 or filamentous algcSy living in intimate connection, and together 



forming a compoimd thallus or * Consortium'' and have been 



so evolved as consortia that it is more convenient to treat them as a 

 separate class .... From the symbiosis entered into by a Lichen 

 Fungus ivith an alga, a dual organism results ivith a distinctive 

 thallus, of which the form (influenced by the mode of nutrition 

 of the independently assimilating alga) differs greatly from that of 

 the non-symbiotic Eumycetes " i. 



These sentences admirably illustrate the manner in which it is 

 usual to teach the Lichen at the present day, emphasizing (1) the 

 marvel of the symbiosis, (2) the 'dual' organization, and, above all, 

 (3) the novelty of the growth-forms thus produced — so distinct 

 from other vegetation — that (4) the plants require to be taken in 

 a special chapter ^ or section ^ away from Fungi proper ; as also they 



1 Strasburger, Textbook of Botany, Engi. Trans, p. 417 (1912). 



' Schenk in Strasburger, loc. cit. 



3 Fiinfstuck in Engler and Prantl (1898-1907). 



