98 MINUTE MARVELS OF NATURE 



amongst which the nuclei or living centres of the 

 grains exist. Of the layers of tissue which con- 

 stitute the cell-wall of each grain, the botanist 



f 



If; 



Fig. 62. Sections of pollen-grains of the mallow flower, showing 

 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 fluid 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, 



