

254 



BOTANICAL GAZETTE 



[APRIL 



secreting. He finds, however, that Prunus laurocerasiis will not 

 begin secretion unless the temperature is 12 C. or over. Haupt 

 (10) also finds that a minimum temperature is necessary to induce 

 secretion. Lepeschkin (14) finds in the hyphae of Pilobolus a 

 secretion steadily increasing with, and much more rapidly than, the 

 absolute temperature. In other cases he finds an optimum above 

 which secretion diminishes. In the case of secreting hairs of the 

 bean leaf this optimum is 20 , in the Abutilon nectary it is 26 . 



Experiments were carried out in uniform temperature incuba- 

 tors. For much of the work, to avoid light exclusion, which is 

 detrimental to secretion, incubators were employed which w r ere 

 specially constructed for the purpose, being covered with two glass 

 plates separated by an air space. 



The optimum temperature for amount of secretion lies between 

 20 and 25 for Cucurbita Pepo, Lilium speciosiim. Carina indica, 

 Euphorbia pidcherrima, and extrafloral nectaries of Impatiens 

 Sultani. For Salvia splendens and most of the Leguminosae tested 



. As a rule, the sugar concentration of the nectar 



1 



:> 



it is about 



does not differ materially for the different temperatures. Typical 

 sugar determinations obtained from the flower of Abutilon striatum 

 are given in table II, the blossoms being quartered and one piece of 

 each placed in each incubator, thereby eliminating any error due 

 to individual variations. 



TABLE II 



Time 



Mg» invert sugar per flower 



io' 



After 36 hours 



After 16 hours (another set) 



10.20 

 3°7 



16 



23 



3°' 



12.00 

 6.57 



16.00 

 12.97 



10.32 

 10.87 



v 



1 





Here the optimum is clearly not far from 



AH 



nectar secretion is greater in the same species at high latitudes and 



altitudes than at low 



grows norn 



compared, and furthermore 



Alps. He 



Norway 





-*- 



