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 Urticacese behave in 

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

 Pilea microphylla (also known under the name of Pilea mMscosa), which grows 



Fig. 229. — The Paper Mulberry-tree {Broussonetia papyri/era). 



I Leafy branch with capitulum of female flowers. 2 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 filaments are 

 still tucked in, one has sprung up and is expelling the pollen from the opened anthers. « An open male flower with all 

 its stamens already uncoiled and the pollen discharged from the anthers. « Two female flowers with long hairy stigmas. 

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



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

 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 

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

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

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

 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 



