rll.] 



POLLEN. OVULES. 



25 



tally adhering to its hairy limbs and body, to the stigma. 

 This transfer of the pollen from the anther to the stigma is 

 highly important. If we separate a few stamens, wA'C^ their 

 anthers and pollen, and keep them apart from the rest of 

 the flower, or if we remove the pistil in the bud so that 

 stamens only remain within the envelopes, we shall find 

 that they ultimately shrivel and wither up, pollen-grains and 

 all, without undergoing further change. But the case is 

 different with the grains of pollen which reach the stigma. 

 After an interval, varying in different plants from a few 

 hours to several months, we find the pollen-grains begin to 

 grow, and their growth takes place in this way : — 



Each grain of pollen, as we have already learnt, is a single 

 cell. These cells almost invariably have a double coat, an 

 outer and an inner; and in the outer coat there are fre- 

 quently thin places, or actual openings here and there, 



Fir,. 12 rt. Diagram representing Pollen- 

 grains upon the stigma of a carpel of 

 Ranunculus, which have developed their 

 tubes, reaching to the micropyle of the 

 ovary. The tubes are so delicate that 

 it is impossible to trace them the whole 

 way. 



Fig. 12 ^. The Stigma magnified, with 

 grains of pollen upon it. 



which permit the inner coat to grow through them at one or 

 more points. This growth of the inner coat of the pollen- 

 grain is encouraged by the moisture which bathes the stigma, 



