TEMPERATTJEE REQUISITE FOR GERMINATION. 465 



clear ice ; the seeds themselves being in hollows on its surface. 

 The temperatiire must of couree be given as 0° C. Uloth found 

 also that wheat-grains germinaterl in the same cellar upon pieces 

 of ice. Kerner ^ placed seeds with some earth in glass tubes and 

 exposed them to the cold springs on the edge of snow-fields in 

 Alpine regions. He found that the seeds of most Alpine plants 

 could germinate at 2° C, and that some might even at 0°. It 

 was shown that at all growing points there is some lieat evolved. 

 In Uloth's observations, above noted, attention is called to the 

 fact that the rootlets descended into solid ice in a number of 

 cj'lindrical cavities which they melted out for themselves. 



1208. The minimum temperature for germination of the seeds 

 of many plants in common cultivation is given by Haberlandt ^ 

 as 4°. 75 C. (although some can start even below this). Be- 

 tween 4°. 75 and 10".5 we have the minimum temperature for 

 Indian corn, timoth\' grass, sunflower; between 10°. 5 and 15°. 6, 

 that for tobacco and squash ; between 15°.6 and 18°.5, that for 

 cucumber and melon. 



1209. The maximum temperature, or that bejond which germi- 

 nation cannot begin, differs greatl}- in different species. Haber- 

 landt has shown that degree of ripeness, freshness, the " race," 

 and several other influences considerably modify the result. 

 The maximum temperature for a few of the more common plants 

 is here noted : — 



c°. 

 Wheat, vye, barley, oats, peas, timothy grass, cabbage, poppy, flax, 



and tobacco 31-37 



Eed clover, lucerne, buckwheat, and sunflower 37.5-44 



Indian corn, millet, squash, cucumber, and sugar melon .... 44-50 



In no case was germination observed above 50° C. 



1210. Between the minimum temperature below which and 

 the maximum temperature above which germination of a cer- 

 tain kind of plant does not ordinaril}' take place there lies an 

 optimum, temperature ; that is, the degree at which germina- 

 tion begins most speedily.^ The short table on the following 

 page is by Sachs : — 



1 Berichte der naturw-med. Vereines in. Innsbruck, 1873, and Botanische 

 Zeitung, 1873, p. 437. 



2 Versuchs-Stationen, xvii. p. 104. 



' The diff'erence in regard to the degree of warmth demanded by seeds of 

 the same species raised in different climates has been examined by Schiibeler 

 (Die Culturpflanzen ISTovwegens, 1862, p. 27). 



30 



