208 



THE REPRODUCTIVE ORGANS 



inverted ovule is said to be anatropous (Fig. 141, 2) (Gr. 

 ana, denoting inversion, trepo = I turn). A straight one 

 is orthotropous (1) (Gr. orthos = straight) ; when curved 

 it is campylotropous (3) (Gr. kampylos = curved) ; and 

 when at right angles to the funicle, amphitropous (4) 

 (Gr. amphi = on both sides). 



Fig. 140. Development of an Ovule. em, embryo-sac ; 

 n, nucellus ; p, outer integument ; s, inner integument. 



Fig. 141. Forms of Ovules. 1, orthotropous ; 2, anatropous ; 

 3, campylotropous ; 4, amphitropous ; em, embryo-sac ; /, funicle ; 

 n, nucellus ; p, outer coat or primine ; s, inner coat or secundine. 



When the ovule has developed thus far it is ready for 

 fertilization. Before this can take place, however, pollen- 

 grains of the same species must be deposited on the stigma. 

 This, when ripe, is covered with a sticky, sugary secretion, 

 in which the pollen-grains germinate. 



Germination of pollen-grains, and fertilization. By means 

 of a simple experiment a good idea may be obtained of 

 what occurs. Place a drop of 10 per cent, solution of cane 

 sugar on a glass slip and put into the solution a few pollen- 

 grains of the Sweet-Pea. If examined after an hour or two, 

 short, delicate tubes called pollen-tubes will be seen emerg- 



