METEOROLOGY. GROWTH OF PLANTS. 485 



lost from frosts that occur at this {jreat elevatjon in the course of 

 the months of November and January. 



CULTIVATION OF THE INDIGO PLANT. 



In Venezuela, in plantations very near the level of the sea, the 

 first crop is cut about eiji^hty days after sowing. The mean tem- 

 perature is there between 81" and SS" Fahr. In other countries 

 where the mean temperature ranges between 72" and 74" Fahr., 

 which must be regarded as the limits to the growth of indigo, the 

 first cutting takes place 3\ months or 106 days after tlie sowing. 

 In India the first cutting seems generally to occur about ninety days 

 after the sowing, and tlie mean temperature of the two winter iriontlis 

 and of the summer months when the crop is on the ground, at Bom- 

 bay is about 76° Fahr. 



I shall terminate this section by calling the attention of vegetable 

 physiologists to a fact which appears to have escaped them. It iij 

 this : that plants in general, those- of tropical countries very obvi- 

 ously so, spring up, live, and flourish in temperatures that are nearly 

 the same. In Europe and in North America, an annual plant is 

 subjected to climatic influences of the greatest diversity. The 

 cereals, for example, germinate at from 43" to 47" or 48" ; they get 

 through the winter alive, making no progress ; but in the spring 

 they shoot up, and the ear attains maturity at a season when the 

 temperature, which has risen gradually, is somewhat steady at from 

 74° to 78"_Fahr. 



In equinoctial countries things pass dif!erently : the germination, 

 growth, and ripening of grain take place under degrees of heat which 

 are nearly invariable. At Santa Fe the thermometer indicates 

 79" Fahr. at seed as at harvest time. In Europe the potato is 

 planted with the thermometer at from 50" to 54" Fahr., and it does 

 not ripen until it has had the heats of July and August. But we 

 have just seen that this plant grows, slowly indeed, but regularly, in 

 places where the temperature, nearlv invariable, does not rise above 

 48.2" or 50" Fahr. 



Germination, and the evolution of those organs by which vegeta- 

 bles perform their functions in the soil and in the air, take place at 

 temperatures that vary between 32" and 112" Fahr.; but the most 

 important epoch in their life, ripening, generally happens within 

 much smaller limits, and which indicate the climate best adapted to 

 their cultivation, if not always to their growth ; for the vine grows 

 lustily in many places where its fruit never ripens. To produce 

 drinkable wine, a vineyard must have not only a summer and an 

 autumn sutTiciently hot ; it is indispensable in addition that at a given 

 period — that, namely, which follows the appearance of the seeds — 

 there be a month, the mean temperature of which does not fall below 

 19" cent, or about 66^-" Fahr., a fact of which conviction may be 

 obtained from the following table which I borrow from M. de Hum- 

 boldt: 



41* 



