44 



Action of Light on Bacillus anthracis. [Feb. 16, 



Selaginella, &c. The tufts of archegonia and antheridia in Mosses* 

 are often orange to red. 



Nor are Algfe wanting in good examples. I take it the oogonia 

 and antheridia of the Characeos are cases in point ; and the yellow 

 pigment accompanying the antherozooids and oospheres of Fucus as 

 they ooze from the conceptacles at low tide probably serves as a 

 colour screen. 



The red stigmas of Gorylus would also seem to be one of many 

 similar cases in point ; but, unless the GrramineaB have their plumose 

 stigmas rapidly withdrawn into the shadow of the palea3, they would 

 seem to be witnesses against me. 



The matter will probably not end with such cases as I have cited, 

 and I am strongly inclined to regard chlorophyll as serving the part 

 of a colour screen in the sense indicated, as well as that of an instru- 

 ment! of assimilation. This is by no means the same as Prings- 

 heims's screen theory of chlorophyll, but it may well be that the 

 great absorption in the blue and violet has a screen effect. 



Some Practical Bearings of the Results. 



The establishment of the fact of the bactericidal and fungicidal 

 action of light, dating from Downes and Blunt to now, enables us to 

 see much more clearly into the causes of several phenomena known 

 to practical agriculturists, foresters, hygienists, &c. 



It helps to explain, for example, why the soil of a forest should 

 not be exposed to the sun, a dogma long taught in schools ; it will 

 also affect our way of regarding bare fallows. It has already been 

 shown how important is its bearing on the purification of rivers, and 

 the reasoning obviously applies to dwellings, towns, &c. I regard it 

 as probably explaining many discrepancies in the cultures of Schizo- 

 mycetes and Fungi in our laboratories, and as having a very im- 

 portant bearing indeed on the spreading of plant epidemics in dull 

 weather in the summer, and no doubt this applies to other cases on 

 which I can speak with no authority. 



That sunshine has something to do with the rarity of bacterial 

 diseases in plants now seems quite as probable as the currently 

 accepted view that the acid nature of the latter accounts for the 

 fact. 



If that part of the chlorophyll which absorbs the blue- violet is a 

 screen to prevent the destruction of easily oxidisable bodies, as they 

 are formed in the chloroplasts, we may reconcile several old experi- 

 mental discrepancies — e.g., the behaviour of plants under bichromate 

 and cupric oxide screens. 



* The calyptra may be of service as a screen in another way. 

 f Elfving also (loc. cit., p. 54) hints that the chlorophyll may serve as a screen 

 in so far as to prevent certain destructive metabolic actions in synthesis. 



