12 W. P. Wilson. 



During the next 14 days the thermometer rose gradually to 13,2° C. at 

 which temperature many of the nectaries began to excrete nectar. A tem- 

 perature of at least 12° C. is required in the case of Prunus laurocerasus» 

 for the metamorphosis of the cell-walls and the raising of the cuticula. After 

 this stage has passed in the activity of the nectary a much lower tempera- 

 ture will suffice for the continued excretion. 



Eifect of Light on the Excretion of Nectar. 



I placed cut flowers from Fritillaria imperialis and Helleborus purpu- 

 rascens, before the buds were open, in a dark room. The flowers opened 

 and secreted nectar as freely as those kept in the light. 



Branches from P. laurocerasus, the nectaries of wiiich were inactive 

 were at the same time placed in a dark and a light room. The temperature 

 was the same in each. There was no observable difference, either in the 

 time when the nectaries began to secrete or in the amount of the excretion. 



In difFused light the excretion of nectar in the nectaries of Eranthis 

 hiemalis was almost zero. The amount was considerably increased when 

 the flowers were placed in the sunlight. 



The nectaries on the leaves of Acacia lophantha which were secreting 

 finely in the sun, when placed 6 meters back from south Windows in 

 diffused light stopped all excretion after from one to two days; while the 

 nectaries on such plants as were left in the sunlight continued active, The 

 plants used were seedlings in pots, 15 to 30 ctm. high. 



The nectaries on the stipules of Vicia faba, on such plants as were 

 grown in the sun, began to secrete nectar when the first leaf was scarcely 

 unfolded, while plants grown five meters back from large south W'indows, 

 but where the direct sunlight did not reach them, never produced nectar. 

 The latter plants, when brought into the sunlight sometimes began to 

 secrete nectar on the first day, and ahvays on the second. Plants grown 

 in total darkness formed the nectaries perfectly, but never secreted nectar 

 until brought into the sunlight. Such wholly etiolated plants secreted ac- 

 tively after from two to three days standing in the sunlight. 



I have repeatedly removed plants of Vicia faba from the sunlight, 

 where the nectaries were very active, into diffused light four or five meters 

 from the Windows and invariably with the same result. 



Drying the nectaries at the time of removal with bibulous paper, I 

 have found that there was no more nectar produced. Perhaps twice in 20 

 repetitions two or three nectaries out of 18 or 20 have secreted nectar 

 under such conditions. It is very probable that in cases where secretion 

 took place the nectaries had not been fully dried. Such plants as have 

 actively secreted nectar in the sunlight and have remained inactive in dif- 



