146 Mr Burkill, On the Fertilisation of some [Feb. 12, 



remains sufficient in the surrounding anthers to ensure self-fer- 

 tilisation. 



Further, if the stigma fails to strike against the insect-visitor, 

 the impact on the vexillum is sufficient in many cases to render 

 the flower fertile. For if the flower be exploded by simply pulling 

 the alae apart it may set seed. The stigma strikes against the 

 smooth and not the rough part of the vexillum. In order to 

 make certain that this was due to the vexillum and not to the 

 edges of the keel, I removed in above fifty flowers the lamina of 

 the vexillum and then exploded them ; out of these none set seed, 

 while out of 34 in which the vexillum remained, exploded at the 

 same time as a control experiment, 12 set seed. Therefore should 

 the insect visitor fail to bring about fertilisation, impact 

 on the vexillum in some extent (here 35Yo) ensures it. 



That the separation of the basal processes is the legitimate 

 and almost only natural method of exploding the flower is obvious 

 from the following consideration. By means of a fine wire hung 

 on to the alae, weights to a known extent were suspended from 

 them. In September 1892 flowers obtained near Poulton (Glou- 

 cestershire) were found to explode with an average weight of 1'68 

 grammes (maximum and minimum 2"37 and "QS). Now an insect 

 visiting the flower rests its weight on the points whence these 

 weights were hung. The worker of Apis I find to weigh about 

 "096 and Bombus hortorura (large specimens) "199 grammes. The 

 mere weight of these two insects is therefore quite insufficient to 

 explode the flower. Moreover the pedicel of the flower bends 

 under a weight insufficient to explode the flower, so that in these 

 experiments I found it necessary always to fix the flower by a 

 wire hooked into the standard ; and again the Hive bee so settles 

 as to hold the parts of the flower together with its feet. 



By the same method of experiment I discovered that the 

 flower is not always in the same degree of explosiveness; 

 the hotter the weather the more explosive is the flower. 

 In cold weather the flower frequently remains unexploded for 

 eight or nine days, after which it withers, but in hot sunny 

 weather I found three days to be the maximum duration; for explo- 

 sion is brought about, — often within 24 hours from the opening of 

 the bud. We must remember in this connection that M. sativa is 

 of Persian origin and has only traversed Europe northwards by 

 slow degrees \ 



Shaking by the wind cannot explode the flowers. Pieces of 

 paper with a surface of 18^ and 22 square inches were tied to stalks 

 of this plant, in order to give more power to the wind, but no 

 effect was observable from the shaking it produced. 



1 Alph. De Candolle. Origin of Cultivated Plants. London, 1884, p. 103. 



