98 MINUTE MARVELS OF NATURE 



amongst which the nuclei or hving centres of the 

 grains exist. Of the layers of tissue which con- 

 stitute the cell-wall of each erain, the botanist 



Fiy. 62. Sections of pollcn-graiiis of the mallow Hower, showinR 

 that the microscopic granules possess the characteristics of 

 vegetable cells 



terms the outer layer the "extine," and the inner 

 the "intine." When a pollen-grain reaches the 

 stigma the viscid Huid which the latter secretes 

 causes a kind of germination to take place, and 

 through certain weak places in the extine layer the 

 intine begins to bulge and gradually forces a way 

 through, assuming the form of a little tube, which 

 increases in length in a very wonderful way, 



