Fruits and Seeds. 191 



in the Lamb's Lettuce,* the fruit contains three 

 cells, each of which would naturally be expected to 

 contain a seed. One seed only, however, is deve- 

 loped, but the two cells which contain no seed 

 actually become larger than the one which alone 

 might, at first sight, seem to be normally developed. 

 We may be sure from this that they must be of some 

 use, and, from their lightness, they probably enable 

 the wind to carry the seed to a greater distance 

 than would otherwise be the case. 



3. In other instances the plants themselves, or 

 parts of them, are rolled along the ground by the 

 wind. An example of this is afforded, for instance, 

 by a kind of Australian grass, in which the mass of 

 flowers, forming a large round head, is thus driven 

 for miles over the dry sands until it comes to a 

 damp place, when it expands and soon strikes root. 



So, again, the " Rose of Jericho," a small annual 

 with rounded pods, which frequents sandy places in 

 Egypt, Syria, and Arabia, when dry, curls itself up 

 into a ball or round cushion, and is thus driven 

 about by the wind until it finds a damp place, 

 when it uncurls, the pods open, and sow the seeds. 



4. These cases, however, in which seeds are rolled 

 by the wind along the ground are comparatively 

 rare. There are many more in which seeds are 

 wafted through the air. If you examine the fruit 

 of a Sycamore, you will find that it is provided with 

 a wing-like expansion, in consequence of which, if 



* Valerianella. 



