DISPERSION OF POLLEN BY THE WIND. 



137 



in another half-hour there is an entire cessation of the phenomenon. On inspection 

 one easily discovers that it depends on the fact that the filaments bearing the 

 anthers are coiled in the bud, and suddenly spring up at the same moment that the 

 dehiscence of the anthers takes place. 



The species of the genus Parietaria and many tropical Urticaceae behave in 

 the same manner in this respect as our Nettles. As an instance may be taken 

 Pilea viicTophylla (also known under the name of Pilea muscosa), which grows 



Fi„'. 229— The Papei Mulbeiry tree (Brotissoiietia papynjei a) 



» Leafy branch with capitulum of female fioweis. - Piece of a branch stripped of its foliage with spike of male flowers. « An 

 unopened male flower in longitudinal section. * An open male flower in longitudinal section; two of the Jilanieuts are 

 still tucked in, one has sprung up and is e.\pelling the pollen from the opened anthers. ' An open male flower with all 

 its stameus already uncoiled and the pollen discharged from the anthers. « xwo female flowers witli long hairy stigmas. 

 1, 2 natural size; s-s x4-5. 



; native in Central America, and is often raised m botanic gardens with a view to 



j demonstrating the phenomenon here alluded to. One only has to sprinkle the 



plant with water at a time when it is covered with flower-buds and then take it out 



of the shade into the sunshine, and the phenomenon is immediately exhibited. All 



I over the plant the flower-buds explode, and a whitish kind of pollen is discharged 



I into the air in the form of a little cloud. Many Moreae also display this 



phenomenon, as, for example, the Paper Mulberry-tree (Broussonetia iDapyrifera), 



an illustration of whose flowers is given in fig. 229. The male flowers are arranged 



in spikes (229^), and each flower consists of a sepaloid perianth with four stamens 



