Illumination and Vegetation. 
2 77 
four different lights, from April 9th to the middle of June. One of 
the trees was placed in the full open light and three others to the 
North, East and South of walls of such height that each received 
about a quarter of the sum of the full diffuse light which fell upon 
the plant in the open. As regards the sunlight none ever reached 
the north plant (N), while the east plant (E) got the morning sun, 
the south plant (S) the mid-day sun, and the plant in the open (O) 
the whole of the sun. 
The first leaf-tip appeared :—N., April 20; E., April 16th ; S., 
April 13th; O., April 13th. The.development of the leaves occupied 
N., thirty days; E., twenty-two days; S., twenty-two days; O., 
twenty-two days. The same numbers of leaves were formed in all 
the positions, but the total fresh weights of leaf were different, 
being N., 52 ; E., 60; S., 74 ; O., 100. 
The conclusion reached is that diffuse light alone suffices for 
normal leaf-development of the Beech, but that direct insolation 
hastens and promotes this development. 
Recently Strakosch 1 has carried out experiments on the 
influence of sun and a diffuse light on that characteristic sun-plant 
the Sugar-beet. 
The shaded plants were under a framework of planks and fine 
gauze, exposed to a light estimated at three-quarters of the total 
diffuse light, and no direct sun. When compared in October with 
the control plants grown in full sunshine, it was found that the 
shaded leaves were 10% smaller and 25% fewer. The difference in 
the roots was very marked, the average weight being 58 gr. in 
diffuse light and 190 gr. in sun, both containing about 12% of sugar 
in their juice. 
Here again the plants come to normal development in diffuse 
light, but are larger in the sun. The marked preponderance of the 
insolated root suggests a direct result of higher temperature of the 
soil in the sun. Of course, one of the main points for critical 
work is to distinguish between the effect of the light of the sun as 
such and the vigorous heat-radiation which naturally accompanies 
it. Such separation could be accomplished by passing the radiation 
through a thin layer of water, but experiments on a big scale have 
yet to be carried out in this way. 
A complete exclusion of sunlight without serious diminution of 
diffuse light could be carried out by means of a sort of “ negative 
heliostat,” a clockwork arrangement which would always cast a just 
1 Qster-ungar. Zeitschr. fur ZucUerindustrie, 1906, 
