176 The Great World's Farm 



Why should the pollen-tube always grow with its end 

 directly towards the very narrow opening by which it is to 

 enter the ovule? 



For the ovule is often far away — what, considering the 

 size of the pollen-grain, may be called, without exaggera- 

 tion, hundreds of miles away — while the door by which 

 alone the tube can find entrance is the merest point. 

 Indeed, the ovules themselves are often mere specks, and 

 usually they are placed in what looks like a most inaccess- 

 ible position, quite inclosed in the ovary. Often, too, 

 there are hundreds, and even thousands of ovules in one 

 ovary, each of which receives at least one pollen-tube, in 

 some cases more. 



Even when it has taken the first turn downwards in the 

 right direction there is plenty of room — either on its way 

 down the pistil stalk or when it reaches the ovary — for 

 the tube to go astray. But instead of doing so it makes 

 unerringly for its mark, and we can only conclude that 

 some definite arrangements exist by which it is directed 

 into, and kept in, the right way. 



QUESTIONS FOR REVIEW 



1. How are different classes of plants affected by the fruit- 

 bearing process? 



2. How do bulbous plants prepare for their bloss6ms? 



3. What peculiarities has the American aloe? 



4. What relation has the size of the blossom to the size of 

 the plant? 



5.- Describe the peculiarities of the largest known blossom. 



6. Describe the chief parts of a flower. 



7. What are double blossoms? 



8. Describe the pollen-grains. 



9. How does the pollen reach the ovules? 



