274 TAKING UP OF POLLEN BY INSECTS. 



pollen is of a floury consistency and is tightly compressed in the anthers, but it is 

 sifted out intermittently, a little at a time, somewhat as powdered sugar is shaken 

 through the holes of a castor. In some cases the anthers are suspended inside the 

 bells with their pores downwards from the very commencement, as, for example, 

 in the flowers of the Snowflake (Leucojum vernum) and those of the Cowberry 

 (Vaccinium Vitis-idcea); but in others the elastic filaments are reflexed and hold 

 the anthers at first with their pores upwards, facing the receptacle of the pendent 

 flower. In order that the pollen may fall out of this class of anthers (with pores 

 directed upwards), they must be turned upside down. This inversion is effected by 

 insects, and as an example we will describe how it occurs in a Winter-green (Pyrola 

 secunda). The filaments are curved into the shape of the letter S and are in a high 

 state of tension, and the anthers borne by them are held in position, with their 

 pores directed upwards, by the pressure of the petals (see fig. 277"). When an insect 

 visits the bell it displaces the petals with the result that the filaments straighten 

 out and the anthers are inverted (fig. 277^). In a large number of instances the 

 anthers are furnished with special appendages against which insects are sure to 

 strike when they enter the flower, whereupon a little pollen invariably pours out. 

 The Snowdrop (Qalanthus) has simple rigid points depending from the free ex- 

 tremities of the anthers and standing in the way of insects, and so also have 

 Cyclamen, Ramondia, and many other plants belonging to widely-different families. 

 The Strawberry-tree (Arbutus) and the Bearberry {Arctostaphylos; cf. fig. 263^ 

 p. 240) have two little horns projecting from the back of each anther, against which 

 insects knock in their quest for honey, the result being that the whole anther is 

 shaken and scatters pollen through its pores. 



Anthers which dehisce by pores and act in the manner above described are 

 usually associated with actinomorphic {i.e. radially symmetrical) and either pendent 

 or nodding flowers, and all the cases we have examined hitherto have in fact been 

 of pendent or nodding bells of perfectly regular conformation. Of the few zygo- 

 morphic flowers {i.e. symmetrical about one plane only) furnished with anthers of 

 the kind I can only refer briefly to the Calceolarise and Melastomacese. In these 

 plants the anthers rest on short filaments, and are easily set rocking like those of 

 Salvia. But whereas in the flowers of Salvia the anthers dehisce longitudinally 

 and contain pollen of viscid consistency, those of the Calceolarise and Melastomacese 

 open by pores, whilst the pollen contained in them is of mealy or powdery con- 

 sistency. The anthers are set swinging by insects knocking against them, and the 

 pores being thus lowered the pollen comes tumbling out on to the bodies of the 

 intruders. 



The third form of sprinkling apparatus consists of a whorl of stiff stamens 

 grouped together so as to form a hollow cone. The anther belonging to each 

 stamen is composed of two lobes which open by longitudinal fissures and after 

 dehiscence are simply open niches. The pollen is in the form of meal or powder, 

 and in order to prevent it from falling out of the niches before the right time a 

 special contrivance is necessary to keep them closed. This result is attained by ' 



