THE FLOWER 



259 



Fig. 242. — A grain of pollen 



of Cucurbita maxima (magni- 



iied 4 80 times). 



Fig. 243. 

 Fertilization of ovule. 



outside (Anona). In the former case they are called introrse, 

 in the latter extrorse. 



(/) Psllen. — The colour of the pollen changes from bright 

 yellow to orange or red and, in some plants, it is even black. 



If we put pollen- 

 grains into water, 



they absorb so much 



of it that they burst. 



The same happens, if 



they are exposed to 



rain or dew while on 



thetlower. Hence, the 



pollen is protected 



from damp in many 



flowers. If we 

 sprinkle some pollen-grains over a drop of 

 very weak sugar and water, they do not burst, 

 but throw out long threads. This is what 

 they also do when they are brought on the 

 sticky end of the pistil. The thread grows downward between 

 the tissue of the pistil until it comes to an ovule, which is then 

 fertilized. 



8. The Pistil.— 



(a) Parts. — The chief part of the 2>istil is the seed-box or 

 ovary, containing tiny seeds or rather ovules, which are destined 

 to -become seeds, when the fruit ripens after fertilization. This 

 can only happen when the pollen is brought into contact with 

 the ovules. Hence, the ovary tapers at its upper end into a more 

 or less slender pillar, the style. To enable the style to hold fast 

 the pollen-grains that happen to fall on it, its end, the stigma, 

 is provided with tiny warts or hairs, which sometimes rnake it 

 look like velvet (Shoeliower), and also with a sticky liquid, which 

 exudes from the surface of the stigma. Some stigmas (Paddy) 

 are feathery. Some tlowers, like the Lotus, have no style; the 

 stigma is then said to be sessile. 



(6) Ovary — The ovary is made up of one or several fruit- 

 leaves or carpels (from Greek karpos ^ivmi). The line in which 



17* 



