294 



LECTURE XIV. 



In the second, which was compiled by Pfeffer, are given determina- 

 tions of the cardinal points made by Sachs (S), de Candolle (C), Koppen 

 (K), de Vries (V). The observations were made on seedlings : the 

 minima and maxima were determined in some cases by the non-germina- 

 tion of the seed, in others (de Vries) by the actual arrest of the growth of 

 the seedling : the optima were determined by the growth of the root 

 (including the hypocotyl) of the seedlings. 



It may be stated as a general rule that the minimum tem- 

 perature is higher for plants belonging to warm climates than 

 for those which belong to cold climates, but this does not 

 hold good with regard to the maximum. 



Since, as we have been endeavouring to make clear, 

 growth is dependent upon the activity of destructive meta- 

 bolism, it might be expected that the relation of growth to 

 temperature would be the same as that of respiration, for, as 

 has been pointed out in a previous lecture (p. 195), the respira- 

 tory interchange of gases affords an indication of the activity 

 of normal destructive metabolism. There is, it is true, some 

 sort of parallelism between the relation of growth to tempera- 

 ture and that of respiration to temperature, but the two are 



