178 
Date of flowering of wheat at Montrouge, France. 
[See Marié-Davy, 1880, pp. 181—215.] 
Shade tempera-| Sun thermom- | Opgery- | Actinometric 
tures. eter. | ed date | percentages. 
Year | of 
Date. | Stal, | Date. | stat | “one.” | dates, | dates 
| | 
oC! Xen 
BGS Sonos hs or as Se fe SO pr June 21 1264 | June 21 1569 June 21 4063 4063 
ee he eee = UNS wo 1268 | June 10 1566\ise2 > ee 3467 3666 
1 ESA fee ore to ie rd SER pe opel gy | Junel2) 1274 | June 15 1578 | June 15 3976 4075 
STG Sees Sea he eins Bele cae ne no een Junel5 |) 1269; Junel9| 1567 | June 19 4376 4588 
bv eos ye pe NY a Date ee ag RUM OP Ri a June 7 1264 | June 13 54s Eee 4298 4603 
LENG eS hg AA ele SO nee nee» RN es June 10 Diop ee a - eee June 9 4506 e/a eee 
Tey Sore eee ee ae ae aes ee, June 19 | 2b6 "| Se ee nee Se cee | Seen 4296 ||| s2o22-= = 
Marié-Davy concludes that by keeping a daily summation of 
actinometric degrees it becomes possible, even at the epoch of flower- 
ing of wheat, to estimate in a very approximate manner what will be 
the final value of the resulting harvest. At this moment, even if we 
have already measured the sum of the products which should be 
applicable to the formation of grain, we can not be absolutely cert. in 
that the harvest will correspond to our expectations. A certain time 
is necessary for the nutrient particles to traverse the various parts of 
the stem up to the seed, and a certain quantity of water is necessary 
for this transportation. An excessive dryness or heat will interfere 
with this movement and will give a poorly developed grain, notwith- 
standing the abundance of nutrition reserved for it within the plant. 
But although water and nutrition are as important as heat and light, 
still we find that predictions based on actinometric degrees alone are 
very reliable. 
According to Georges Coutagne, the law that connects the rate of 
development of a plant with its temperature must be such that it has a 
maximum value for a special temperature and diminishes as we depart 
from this down to a zero rate at the freezing point and also to zero 
at some higher temperature at present unknown; all this is on the 
assumption that the sunlight, moisture, and winds are such as to 
enable the plant to do its very best at the given temperature. If 
this law were known we could then determine whether a plant would 
live and flourish in any given climate. 
This law of growth has been expressed by Georges Coutagne, as 
quoted by Marié-Davy (1883, p. 227), by the following notation and 
formula. Let— 
v» be the rate of development of the plant, assuming that other 
conditions are so adjusted that it attains the maximum growth 
possible for the given temperature; 
x be the temperature of the plant; 
