1910. | On Vegetable Assimilation and Respiration. 405 
in water-plants. Pantanelli’s ultimate object was the investigation of the 
effects of intense light upon chloroplasts and their power of assimilation. 
He is interested to see whether the decline of assimilation in “ ultra-optimal ” 
light is correlated with bleaching of chlorophyll, aggregation of plastids, and 
inhibition of protoplasmic circulation ; and he rightly attaches great import- 
ance to the functional activity of the colourless protoplasm of the plastid. 
Too readily, however, he shelves complex phenomena as due to “ irritability,” 
and interprets his effects generally in terms of fatigue of the plastid by the 
strong stimuli of intense light. He would define the optimum as the 
maximal intensity of function which can be carried on for an appreciable 
time without fatigue. 
We propose to show how, in our opinion, the data which Pantanelli 
presents in illustration of his principles can be more clearly and satis-_ 
factorily interpreted from the point of view of interaction of limiting 
factors. Let us take first the curve which he puts forward for the relation of 
the rate of bubbling to different intensities of light. On Plate 4, Elodea, a, 
Pantanelli gives a graphic diagram which represents the bubbling in a series 
of lights ranging from 1/36 sunlight to 64/1 sunlight, being the mean of 
all the experiments carried out in less than 15 vols. COz per 100 c.c. water. 
The enclosed part of the diagram in our fig. 8 represents Pantanelli’s curve 
in slightly modified form (cf. p. 408); the abscissee are intensities of light, 
and the ordinates the times in seconds for the liberation of 10 bubbles. 
Pantanelli’s interpretation of his results being based upon the conception 
of optima, he naturally finds it difficult to apply such interpretation 
precisely over a wide range of conditions. He has no thought of abandoning 
this point of view as untenable, and he is therefore driven to hold that the. 
optimum of one factor may be shifted considerably by alterations in the 
magnitude of the other factors, so that the position of the CO:-optimum 
becomes purely relative to the magnitude of the light-intensity, and so 
on.* This can only be regarded as a transitional point of view and cannot 
be even a temporary halting place. 
The lights he investigated ranged from 1/36 sunlight to 64/1 sunlight 
(see footnote, p. 408) and the CO.-supply from 1 to 50 vols. per 100 ce. 
of water. As regards the factor of temperature we have unfortunately 
| inadequate information, because Pantanelli’s research was carried out before 
t 
* He says: “The light optimum for Elodea, etc., is about 1/4 sunlight in spring water, 
and shifts towards stronger light with increase of the CO,-content, and towards weaker 
light with decrease of CO, ”—p. 224. “ With 1/4 light CO,-optimum is about 10 vols. CO, 
per cent.; with 1/1 light, 15 vols. CO, per cent. ; and with 4/1 light, about 20 vols. CO, 
per cent.”—p. 195. 
