President's Address. 329 



the oil globules, the tannin vesicles, — are unaflfected by exposure to 

 intense light. 



Starch grains in the chlorophyll-corpuscles have the same appear- 

 ance, and exhibit the same reaction with iodine, after, as before 

 insolation, and the same is true of the starch in the amylum bodies 

 of Spirogyra. With the destruction of the chlorophyll colouring 

 matter no formation of starch is associated. If starch was present 

 in the chlorophyll-corpuscle before insolation, it is found in like 

 amount afterwards ; if there was none before insolation, none is 

 found afterwards. There is neither destruction nor formation of 

 starch as the result of exposure to intense light. This is no contra- 

 diction to the well-known fact of the accumulation of starch in the 

 chlorophyll-corpuscles during the day. For the explanation of that 

 is very simple. Starch is not directly formed from the decomposi 

 tion of carbonic acid and water ; and, if in light of no great 

 intensity there is an accumulation of starch in the chlorophyll- 

 corpuscles, it happens because the light was not sufficiently intense 

 to destroy the formative material out of which the starch is con- 

 structed. 



Oil globules, both within and outside the chlorophy llcorpuscles, 

 behave in every respect like starch. At least all the colourless and 

 oil-like globules, such as occur in the bands of Spirogyra, in the 

 chlorophyll-corpuscles of CJiaracece, Vaucheria, Fontinolis, &c., 

 which are to be considered as of a fatty and not of a volatile oil, do. 



Tannin vesicles of Mesocarpvs are indestructible by light alone. 

 They are, as already noticed, very sensitive to hurtful agencies, and 

 when the cell is killed by light they are, of course, decomposed ; 

 but this is rather a secondary effect, the result of the death of the 

 cell, which has been already brought about by light. 



Hypochlorin, on the other hand, disappears from cells exposed to 

 intense light, and no trace of it remains. If a filament of (Edogonlum, 

 Spirogyra, Cladophora, or Mesocar2ms be exposed to intense light, 

 there is decolorisation of the insolated area ; the cells of the rest of 

 the filament are unchanged. If now dilute hydrochloric acid be 

 added hypochlorin appears in the usual way, after from six to 

 twenty -four hours, in the non-exposed areas, but none is seen over 

 the insolated portion. If, in Spirogyra, insolation is interrupted 

 before the chlorophyll colouring matter of the bands is dissipated, 

 no hypochlorin is found on the slightly or half decolorised bands, 

 though it is present on the non-insolated bands. Five or six 

 minutes of insolation suffice to decolorise the bands of Spirogyra 

 jugalis; under the same conditions two or three minutes are enough 

 for the destruction of the hypoclilorin. Where there are isolated 

 chlorophyll-corpuscles the same is observed, e.g., if a portion of a 



