90 
BOTANY: OSTERHOUT AND HAAS 
tuting in this equation the values of M and T we have 20.4 K = 1 whence 
K = 0.049. 
At the start of the reaction the value of M is 0: this gradually increases to 
1 and remains constant. During this period of increase the value of M may 
be calculated as follows: When M has reached its constant value (M = 1) 
let us suppose that the reaction S — > M suddenly stops while M — > P con- 
times; we shall find that if T minutes have elapsed after this occurrence, the 
amount of M which has disappeared is 1 — e~ KT . If the reaction S — > M 
had not stopped it would have produced enough of M so that (in spite of the 
fact that M is constantly decomposing) the amount of M remaining at the 
time T would be just enough to balance the loss, or 1 — e~ KT . Hence if we 
start with nothing but S (the values of M and of P being zero) the amount 
of M present after the lapse of any given time T will be 1 — e~ KT and the 
amount of P will be 
p = KT - (1 - e~ KT ) 
This becomes the same as the equation 
when in the latter we put K = A as was done in making the calculations 
given in table 1. Hence when we substitute the value K = 0.049 in the 
equation P = KT — (1 — e~ KT ) we obtain the values already given in 
table 1. 
If the chlorophyll takes part in the reaction by decomposing or by com- 
bining (as some recent evidence indicates), we might suppose that S repre- 
sents inactive chlorophyll, M active chlorophyll and P a derived substance 
which combines with C0 2 . At present it does not seem profitable to at- 
tempt a more extended discussion of this question. But it may be pointed 
out that (as one of us has recently emphasized) 13 consecutive reactions of the 
type here discussed, are to be looked upon as the rule, rather than as the 
exception, in living matter. 
It is evident that either of the theories developed above gives a quantita- 
tive explanation of the results. Both seem to be based on reasonable assump- 
tions. Future investigation must decide which is more useful. 
In any event, it is clear that much is to be learned concerning the dynamics 
of photosynthesis, and it is hoped that the considerations here set forth 
may be of value in this connection. 
Summary. — Viva which has been kept in the dark begins photosynthesis 
as soon as it is exposed to sunlight. The rate of photosynthesis steadily in- 
creases until a constant speed is attained. 
This may be explained by assuming that sunlight decomposes a substance 
whose products catalyze photosynthesis or enter directly into the reaction. 
Quantitative theories are developed to account for the facts. 
