III.] 



A BUTTERCUP. 



undergoing further change. But the case is* different 

 with the grains of pollen which reach the stigma. After 

 an interval (varying in different species from a few hours 

 to several months) we find the pollen-grains begin to 

 grow 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 frequently thin places, or actual openings here and 

 there, which permit the inner coat to grow through it at 

 one or more points. This growth of the inner coat of the 

 pollen-grain is encouraged by the moisture which bathes 

 the stigma, so that at length it protrudes, and, like an 

 excessively minute root-fibre, penetrates the substance 

 of the stigma, and passes down through the very short 

 style, until it reaches the cavity of the ovary. As the 

 changes of which we speak can only be observed under 

 a considerable magnifying power, we shall explain them 



FIG. $a. Diagram representing FiG^S^. The stigma magnified, 



pollen-grains upon the stigma with grains of pollen upon it. 



c f a carpel of Buttercup, which 

 have developed their tubes, 

 reaching to the micropyle of 

 the ovule. The tubes are so 

 delicate that it is almost impos- 

 sible to trace them the whole 

 way in the Buttercup. 



more clearly by reference to the cuts, which represent 

 some grains of pollen which have developed tubes reach- 

 ing into the ovary. 

 4. The ovary contains a minute seed-bud, the ovule, 



C 2 



