266 



TAKING UP OF POLLEN BY INSECTS. 



pollen takes place spontaneously; but a sudden opening of the corolla-limb is caused 

 if a small bee or fly chances to touch the top of a closed flower on its way to visit 

 an open one, and the insect is then dusted with pollen from below as is shown in 

 fig. 274 \ The subsequent events occurring in these flowers will be described later 

 on, and an explanation of fig. 272 5 will then be given. 



The species of the genus Schizanthus, indigenous to Chili and Peru, one of 

 which Schizanthus pinnatus is cultivated in our gardens as an ornamental plant, 

 have long been known to possess mechanism for the explosive distribution of pollen. 

 The most conspicuous object in the open flower of any c ^lants is a single 



up-turned speckled lobe, whose function it is to attract Beneath it are 



two smaller incised lobes which form a sort of keel, affox^^^g ^ ^nvenient place 



Fig. 273. Explosive apparatus in a papilionaceous flower. 



i Flower of Spartium scoparium (Sarothamnus scoparius) seen from the front, the keel closed. 2 Same flower with the keel 

 open ; the stamens previously concealed there together with the style have sprung up. Side view of the same flower 

 after the opening of the keel and springing up of the stamens. * One of the two component petals of the keel seen from 

 within. 



for insects to alight on. Fixed firmly in the furrow of this keel are two 

 stamens, which are released the moment an insect settles on the keel and intro- 

 duces its proboscis underneath the vexillary petal above described. The stamens 

 then spring up, and the pollen is scattered out of the anthers. 



The occurrence of a similar up-throwing of pollen in the flowers of the Yellow 

 Corydalis and a few other species of the same genus (Corydalis lutea, G. ochroleuca, 

 C. acaulis) has been already noted (p. 228) in the account given of the stirrup- 

 shaped lobes on the sides of those flowers. We have only to add that the 

 articulation of the projecting left-hand petal to the two contiguous median petals 

 forming the saddle ceases the moment an insect sprawls upon the saddle and 

 inserts its proboscis underneath the spurred petal. This disconnection has the 

 immediate effect of causing the saddle to drop and the stamens hitherto concealed 

 in the cavity to spring up. The meal -like pollen of Corydalis being liberated 

 early, is by that time lying loose upon the anthers, and is ejected upon the under 

 surface of the insect when the stamens are thus suddenly released (cf. figs. 25 7 3 

 and 257 4 , p. 226). 



