1915] CURRENT LITERATURE 67 
role of the fungi in endotrophic mycorhizas, as in Acer. The only adverse criti- 
cism to be made of this excellent paper concerns the mere detail of the use of 
the words symbiosis and heterotrophic. Heterotrophic is used for the case 
(Tilia) where the same root has ectotrophic and endotrophic mycorhizas, 
which certainly is not the usual sense of the wo oth McDovucatLt and 
Fucus contrast parasitism and symbiosis, ae aad and the best 
usage make parasitism a kind of symbiosis.—H. C. Cow 
Photo-growth reaction—BLAAUW,” who has already eee himself a 
master in phototropism, now publishes an excellent piece of work on the 
effect of illumination on the growth of the sporangiophore of Phycomyces. 
He uses the term “‘photo-growth reaction”’ to indicate the changes in growt 
rate and amount caused by a single short application of light. He first works 
with equilateral illumination applied at right angles to the organ from four 
or eight directions. The quantity of illumination in the different experiments 
varies from 1 to 7,680,000 M.K.S. In all cases an early acceleration in growth 
is followed by a later retardation. In illumination of 16 M.K.S. and above 
the acceleration begins about 3. 5 minutes after the beginning of illumination. 
In 1 M.K.S. it begins after 8 minutes, and in 6 M.K.S. after 6 minutes. The 
maximum acceleration was at about 7 minutes in 16 M.K.S. and above and 
later in lower quantities, Then follows a gradual fall in growth rate until a 
rate considerably below the normal is reached, and then a gradual rise until 
the normal rate is again reached. The duration, amount, and overlapping 
ef these reactions vary much with the amount of illumination. In some of 
the lower light amounts the total acceleration exceeds the total retardation 
by threefold, while in the higher amounts the latter exceeds the former. T his 
agrees with the finding of Jacost that slight illumination (low intensities of 
medium duration or high intensities of short duration) accelerate growth, 
while medium or great amounts of illumination retard growth. Jacost deals 
with only the difference of the accelerating and retarding effects, since she took 
her readings 24 hours after exposure. BLAAuw’s work gives the continuous 
curves. In all the older works only the retarding effect had been reported. 
Biaavw finds that for low light quantities, where the accelerating does not 
quantity of stimulus and quantity of acceleration. The increased growth is 
Proportional to the cube root of the light amount. Jacost’s conclusion 
that the quantity of stimulus law does not apply here is due to her failure to 
recognize that both effects (accelerating and retarding) appeared in every 
application, and that she was dealing only with their difference. 
In a second group of experiments BLAAUw deals with phototropic response 
in the same organ, and with good evidence comes to the conclusion that photo- 
tropism in this form can be explained entirely by the total of the “photo- 
. Stowth reactions.” This brings us back to the old view of De CANDOLLE under 
* BLaauw, A. H., Licht und Wachstum I. Zeitsch. Bot. 6:641-703. 1914. 
