178 



Date of floircriiifi of irhcat at Moiitroiige, France. 

 [See Marie-Davy, 1880, pp. 181-215.] 



Marie-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 

 wdth 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 Marie-Davy (1883, p. 227), by the following notation and 

 formula. Let — 



r be the rate of development of the plant, assuming that other 

 conditions are so adjusted that it attains the maximum gi-owth 

 possible for the given temperature ; 



X be the temperature of the plant; 



