TRANSACTIONS OK SECTION K, 



sol 



5. Resistance of Seeds to High Tem})eratures. By Henry H. Dixox, D.Sc. 



"Various experimenters Lave investig.ated tho limits of temperature which 

 spores of the lower plants and animals can withstand. The results they have 

 obtained show that these spore*, if dry, can germinate after exposure to the lowest 

 temperatures obtainable, while the upper limit for similarly dried spores lies 

 between 100° t'. and l.TO° 0. 



For seeds of the higher plants also it has been more recently shown that the 

 lowest temperatures available are without harmful effects. This note contains 

 an account of some experiments ou the maximum temperatures seeds can with- 

 stand and after which they will retain their germinative power. 



Before exposure to the high temperatures the seeds were either desiccated over 

 sulphuric acid, or dried in an oven the temperature of which was gradually 

 raised to 90° C. After desiccation the seeds were exposed for at least one hour 

 to the higher temperature. After exposure the seeds were sown on moist sand. 

 The following temperatures were obtained as the highest after exposure to which 

 the seeds of the species mentioned could germinate : — 



Mimulus moschatus . 

 M. luteus . 

 Papaver somniferum . 

 P. nudicaule 

 Meconopsis cambrica 

 Schlzopetalon walkeri 

 Brassica rapa 

 Eschscholtzia californica 

 Lactuca sativa . 

 Ilelianthus argophyllus 

 Lolium perenne . 



10.5° 

 112° 

 ]()0° 

 100° 

 100° 

 105° 

 110° 

 110° 

 114° 

 110° 

 110° 



c. 



Medicago sativa . . 121° C. 



Avena sativa . . . 118° 



Hordeum distichum . . 11S° 



Cucurbita pepo . . . 112° 



Helianthus annuus . . 112° 



Pisum sativum . . . 112° 

 Trigonella fenum-graecum 90° 



Lotus tetragonolobns . 100° 



(Jonvolvulus tricolor . . 120° 



Micotiana tabacum . . 112° 



Galtonia candicans . . 105° 



Seeds o{ Lctf/enaria vulgaris and Ilcraclenm (jiganteian were unable to germinate 

 after exposure to a temperature of 90° C. 



The seeds of any one species show considerable individual differences in their 

 power of resisting high temperatures. Thus a large percentage of a sample of 

 seeds, say of Acena sativa, will germinate after exposure to a temperature of 

 100° C.-105° C, while onlv a very small percentage will germinate if exposed to 

 118° 0. 



The time needed for germination is increased by exposure to temperatures 

 near the maximum. In a general way the higher the temperature to which the 

 seeds are exposed the longer will be the period of germination. 



Long exposure to a comparatively low temperature may prove more fatal 

 than a short exposure to a high temperature. Thus seeds which will germinate 

 successfully after one hour's exposure to 110°-120° C. will not germinate after 

 twelve days' exposure to a temperature of 95°-97° C. 



6. The Effect of Temjyerature on Carbon Dioxide Assimilation. 

 By Miss Gabrielle L. C. Matthaei. 



This investigation differs from any which have preceded it on the same subjec 

 in the attention paid to uniformity in the environment of the leaves before the 

 experiment. Recent work has shown that both the assimilation and the respira- 

 tion of a leaf depend on its previous nutrition and temperature. For this reason 

 a separate leaf was used for each temperature, care being tahen to keep them for 

 some time tinder exactly similar conditions. 



Leaves of the Cherry Laurel (Prunus hairocerasns) were employed throughout. 

 Since allowance had to be made for the respiration, this was taken for each' 

 temperature under exactly similar conditions to those existing in the correspond- 

 ing assimilation experiments. A good curve showing the gradual increase of the 

 respiration with the temperature was obtained. 



