: 260 
the complement of the cloudiness and represents the relative duration 
of sunshine, but owing to the varying altitude of the sun can by 
itself alone give no idea of the intensity of the radiation received by 
the plant. To obtain this !sst item and as no actinometric observa- 
tions were made at Arras I give in the fifth column the results of 
observations at Montsouris, expressed in actinometric degrees. 
The beets are reported to have sprouted very late and very un- 
equally; this was due not to dryness, since the rain during March and 
April was in excess of its normal value, but was directly traceable to 
the low temperature, which was especially low in April. 
The study of the development of sugar, week by week, as given in 
the last two columns of the above table shows that after September 9 
the sugar crop increased slowly, became stationary, and then fluctu- 
ated very much as the weight of the leaves fluctuated. The rainfall 
had at that time become light and the development of the beet seemed 
to depend mostly on the temperature, so that it may be concluded that 
the beet ceases to increase in its quantity of sugar after the mean 
daily temperature falls below 13.1° C., and that there is no probable 
advantage in leaving the beets in the soil after that date, which in 
this case is September 29, 1879. 
Marié-Davy points out that the actual increase per decade of the 
weight of the roots coimecides with the increase of the rainfall and 
the temperature, but the proportion of sugar increases with the degree 
of radiation or total sunshine; the sunshine precedes the formation 
of sugar, since its action is slow and indirect, being through the 
assimilation that takes place within the leaves. It is therefore not 
an excess of water, but a deficiency of hght and heat that causes rainy 
autumns and summers to give poor crops of sugar. Therefore, if 
during dry, clear, warm summers having large radiation, one could 
irrigate the fields properly one would realize the best conditions for 
a good crop. Therefore, every ray of sunshine that strikes the 
ground instead of the leaf is a loss to the formation of sugar and by 
helping to evaporate the moisture of the soil it also causes further 
great loss of sap to the plant. These conclusions agree with other 
experiments made by Pagnoul, who raised beets both in darkness and 
under a transparent bell glass, and again in the free air, and found 
the amount of sugar to increase with the strength of the sunshine. 
The following table gives a general survey of the beet crops in Pas 
de Calais and the corresponding climatic data at Montsouris, which 
is about 90 miles south of Arras. The numbers given in the columns 
Yor quantity and quality of the crops are the estimates obtained from 
many planters and are recorded on the following scale: 1, very small 
