422 APPENDIX 



in numbers of crustaceous thalli, there is evident, by normal or abnormal' 

 development, the first advance to the formation of rudimentary squamules, 

 a condition diagnosed as subsquamulose. "Deterioration" of the lichen 

 plant — when it occurs owing to unfavourable conditions — is a reversion to 

 the leprose early stage of the association ; there is no evidence of reversion 

 from fruticose or foHose to squamulose. A glance at the table of lichen phyla'' 

 shows progression again and again from the crustaceous forms onwards. 

 In such a phylum as Physciaceae (with colourless polarilocular spores) there 

 is a clear example of a closely connected series; the different types of 

 thallus — crustaceous, squamulose, foliose and fruticose^are all represented 

 and form a natural sequence, being well delimited by the unusual form of 

 the spore and by the presence of parietin in thallus or apothecium. 



That there has been development seems absolutely certain, and that 

 along the lines sketched in the chapter on phylogeny. Progress has been 

 mainly in the thallus, but there has also been change and advance in the 

 reproductive organs, more especially in the spores which in several families 

 reach a size and septation unparalleled in fungi. That association with green 

 algal cells stimulated the fungus to new development is the view taken of 

 the lichen plant and emphasized in the present volume. But it seems more 

 in accordance with the polyphyletic origin and recurring parallel development 

 in the phyla that association began at the elementary crustaceous stage, and 

 that the lichen soma was gradually evolved within what is after all a very 

 limited and simple structure. 



ADDENDUM 



Foot-note to Page 404 



E. M. Holmes^ has published recently an account of a substance which seems in some 

 respects to answer to the description of manna (Exodus xvi. ; Numbers xi.) more nearly 

 than the generally accepted Lecanora esculenta. The information is quoted from Swann's 

 book: Fighting the slave-hunters in Central Africa. The author writes (p. 116): "I was 

 shown a curious white substance similar to porridge. It was found early in the morning 

 before the sun rose. On examination it was found to possess all the characteristics of the 



manna of the Israelites. In appearance it resembled coriander seed, was white in 



colour like hoar frost, sweet to the taste, melted in the sun and if kept over night was full 

 of worms in the morning. It required to be baked if you intended to keep it for any length 

 of time. It looked as if it was deposited on the ground in the night." The writer has 

 suggested that "the substance might be mushroom spawn as, on the spot where it melted 

 tiny fungi sprung up the next night." Swann's statement has been confirmed by 

 Dr Wareham, a medical missionary from the same district, who states, however, that it is 

 of rare occurrence. 



' See p. 271 ante. " See p. 302 ante. 



^ Chemist and Druggist, xcil. pp. 25-26^ 1920; Bot. Abstracts, N. 903, p. 135, 1920. 



