36 



tion at this temperature is as folloAvs: Lejndinm^ 1.5 da3^s; Sinapis, 

 1.7 days; TrifoIiu?n, 2.6 days; Sescunum, 8 days; Linu7n, 3 days; 

 Iheris, 4 days; Zea mays, 3.75 days; CoUomia, 5.5 days; Nigella, G 

 days; Melon, 9.25 days. 



(7) The relation between temperature and the time required for 

 germination is such that the time is shortest at a certain best tempera- 

 ture for each seed and increases to infinity or impossibility as we 

 depart from that temperature toward the maximmn and minimum 

 limiting temperatures. All calculations of the sums of daily tem- 

 peratures, both in geographical botany, in agriculture, and horticul- 

 ture, are complicated by hypotheses and affected by many causes of 

 inaccuracy, so that De Candolle hesitates to draw very precise con- 

 clusions from his laborious experiments. However, he shows that 

 if the duration required for germination as expressed in days is mul- 

 tiplied by the corresponding temperature expressed in degrees Centi- 

 grade we shall then obtain much more consistent figures if the tem- 

 peratures are counted from the minimum for each plant instead of 

 from the zero of the Centigrade thermometer. The tables on pages 32 

 and 33 give the temperatures and the durations in days, as observed by 

 De Candolle for the species experimented upon by him. For three of 

 these he adopts as the starting point of his calculations the following 

 minimum temperatures — viz, for Lepidium, 1° C. ; for Trifolium 

 repeiiH, 5.5° C. ; for Sesamum., 11° C. 



(8) "Wlien seeds are subject to variable temperatures, as occurs to 

 a slight degree in these experiments, and to a still larger degree in 

 nature, the so-called useless or ineffective temperatures may be in 

 fact unfavorable and even retard the germination, since moisture con- 

 tinues to be absorbed into the seed, although the latter can make no 

 use of it. 



(9) There is some analogy between the germination of seeds and 

 the hatching of eggs. Thus Millet and Robinet have shown that the 

 hatching of the eggs of the silk worm requires at least a temperature 

 of 9° C., and that as the temperature increases above this the num- 

 ber of days required to hatch diminishes faster than required by a 

 constant sum total, so that at a temperature of 20° C, ten days accom- 

 plishes more than twenty days will do at a temperature of 10°. This 

 shows an influence of the minimum temperature similar to that for 

 the seeds of plants. 



An entirely analogous case has been worked out by the author with 

 regard to the hatching of the eggs of the grasshopper when deposited 

 in the soil of our western j^lains. The details of this study will be 

 found in the First and Second Reports of the United States Ento- 

 mological Commission, and afford an illustration of the possibility 

 of making from meteorological data a prediction as to the hatching 



