THE PROBLEM 47 



grain has to send out a tube long enough to 

 reach all the way down the style and into the 

 ovary, till its tip can enter an ovule. In a large 

 Lily, for example, the distance which the pollen- 

 tube has to cover may be quite six inches, a 

 long way for so small a thing to have to grow. 

 Thus the growth of pollen-tubes is a much more 

 serious business in plants with closed ovaries 

 than it is in those with exposed ovules, to which 

 the pollen can be brought directly. 



Ovaries, however, are important in other 

 ways too. They protect the seeds while they 

 are ripening (though the scales of a Gymno- 

 sperm-cone can do this also), and when they 

 have developed into the fruit, they assist in 

 dispersal in many different ways, sometimes 

 by violently splitting open and acting like a 

 catapult (as in Balsams), sometimes by at- 

 tracting birds or other animals who eat the 

 fruit and scatter the seeds (as in Gooseberries 

 or Cherries), sometimes by developing hairy 

 tufts, or parachutes so that the fruit can sail 

 in the wind (as in Thistles). In these last cases 

 and many others, the ovary or seed-vessel en- 

 closes only a single seed, and does not split 

 open, but the whole fruit is sown. It is con- 

 sidered a bad mistake in botany to call the fruit 

 of a Dandelion or a grain of Wheat a seed, but 

 from the plant's point of view there is not much 



