308 THE JOURNAL OP BOTANY 



must overcome successfully, not only in considerable numbers but for 

 very long periods to produce elodes. We might fairly ask, if elodes 

 sprang from macula fa in the past, why do we not find forms of 

 maculata at the present time on heath-land in various stages of transi- 

 tion ? In any case a long period would be required for maculata to 

 be transformed into elodes, and a still longer one for the whole 

 constitution of the plant to be so completely changed that it cannot 

 exist on the parent-soil from which it sprang. We are thus driven to 

 the conclusion that the ancestor from which it was derived was a 

 distant one. It has been observed that the most nearly allied species 

 occupy different areas. The natural explanation appears to be that 

 they are descended from a remote ancestor which occupied both areas, 

 whose descendants in each area became gradually differentiated till 

 they diverged into two distinct species. It seems more probable that 

 both maculata and elodes have sprung from a distant common 

 ancestor equally at home on peat or chalk or basic soils, and have 

 been modified by gradual adjustment to their respective environments, 

 than that maculata itself has remained unchanged in form and 

 habitat, but has given rise to a variety which can only flourish on an 

 alien geological formation. 



To say that elodes is only a " soil form " of maculata is to beg 

 the question. Even assuming that the differences between them are 

 entirely due to the influence of the soil, this influence must have been 

 exerted for a very long period to produce the considerable morpho- 

 logical differences between them, and this points to a very ancient 

 divergence. If both are " soil forms," seeds of maculata sown on 

 peat should vary in the direction of elodes, and those of elodes sown 

 on chalk etc. in that of maculata. But though millions of seeds of 

 each species must annually fall on areas occupied by the other, each 

 still remains constant to its own habitat, and in the few localities 

 where they happen to grow together, each species maintains its own 

 characteristics. 



PLANT DERMATITIS. 

 By T. A. Sprague, B.Sc, F.L.S. 



Dermatitis is known to be caused by numerous Anacardiacece 

 not included in Miss E. P. Smith's list (Journ. Bot. 1920, 175). 

 Eeuillee, who visited South America in 1702-12, related that some of 

 the seamen of his ship suffered severely as the result of cutting down 

 some " Llithi " trees (Lithrcea caustica) on the coast of Chile. By 

 the following day their heads had swollen to an extraordinary size, 

 and their features had become indistinguishable ; and they might 

 have been taken for monsters rather than men (Obs. ii. 33, t. 25, 

 fig. dextra ; 1725). 



According to Molina (Hist., Engl. ed. 144 ; 1809), "the effluvium 

 from this tree, especially in summer, produces painful pustules and 

 swellings on the hands and faces of those who stop beneath its shade. 

 This effect is various, however, with various persons : there are some 



