830 



MECHANICS OF GROWTH, 



The first point to determine is, whether germination — /. e. the growth of the embryo 

 at the expense of the reserve materials in the seed — talces place only at certain tempera- 

 tures, and at what temperature it takes place most quickly. Observations of my own 

 gave the following results :- 



This table shows, if the ascertained temperatures are correct, that grains of Wheat 

 cannot germinate below 5° C, or seeds of the Gourd below 137°, &c., however long they 

 may lie in moist earth ; and that they no longer germinate, but quickly perish at tempera- 

 tures above those named in the third column ; while at the temperatures named in the 

 second column germination takes place in a shorter time than at either higher or lower 

 temperatures. It may however be taken for granted, from the great difficulty of obtain- 

 ing these numbers, that the result of further observations will not be identical, though 

 probably approximate. It is clear that many series of experiments will be necessary 

 in order to determine each of the cardinal points. The following figures, obtained by 

 Koppen, agree moderately well with mine, as far as they relate to the same plants : — 



Linum usitatissimum 



27-4 



above 3 7 '2 



The following results^, obtained byAlphonse de CandoUe, are moderately trustworthy 

 as far as relates to the inferior limit, but hardly so much so with respect to the superior 

 limit and the temperature of most rapid growth, as may be concluded from various 

 statements made by the observer. 



* I take the figures from the table of curves in De Candolle's treatise, with the assistance of 

 the text. 



' De Candolle remarks that the seeds of Maize, Melon, and Sesamum become brown, the first 



