410 THE BIOLOGY OF FLOWERING PLANTS 



In the. violets the fruit opens by three valves, and the 

 polished seeds lie in these little boats after opening ; 

 gradually the edges of the valves shrink inwards and squeeze 

 the seeds, till finally they are flipped out. In Oxalis the 

 fruit again opens by valves ; the seed has an elastic envelope 

 of arillar nature which, often as the result of a slight touch, 

 slips back and squirts the seeds out. 



In these cases the tissues concerned with the " catapult " 



Fig. 65. — Capsules of Lychnis Flos-jovis : i, dry, with teeth reflexed ; 

 2, wet, teeth closing capsule mouth. Nat. size. 



movement are non-living, and the effective shrinkages and 

 tensions are due to drying. In a smaller number of fruits 

 the action of turgor tensions in a living tissue has similar 

 effects. The most familiar example is that of the touch 

 me-not, Impatiens noli-me-tangere. The five rather fleshy 

 valves of the capsule possess each a layer, under the epiderm, 

 with a very high turgor pressure and elastic walls. As the 

 fruit ripens, the valves become separated from the internal 

 septa, and are held together only very slightly, so that a 



