THE DISPERSION OF SEEDS AND SPORES. 59 



violently thrown out in various directions. The 

 fruit of the common dog-violet (Viola canina) is 

 especially interesting. Each of its three valves, 

 when the fruit opens, has a double row of seeds. 

 The valves are boat - shaped ; in drying they 

 contract till the seeds are all so closely jammed in, 

 and the tension becomes so great, that the slightest 

 touch causes those contained in one of the valves to 

 be shot up into the air. Perhaps the arrangement 

 in the violet regulates the discharge of the seeds, 

 and insures that they are not all scattered simul- 

 taneously. This, at least, appears to be the explana- 

 tion of the peculiar porous dehiscence of the poppy 

 capsule, which is also hygroscopic. The pepper-box 

 arrangement is advantageous, in view of the immense 

 number of small seeds contained in the poppy cap- 

 sule, and insures their widespread and gradual 

 distribution. Possibly a similar purpose may be 

 served by the successive dehiscence of the anthers 

 seen in such flowers as Parnassia, Saxifraga, and 

 Ruta. 



Dehiscent fruits, as a rule, exhibit the hygroscopic 

 character to a greater or less extent. Indehiscent 

 and schizocarpic fruits do not possess it to the same 

 degree. Where a fruit only contains one seed there 

 is no reason why it should open to discharge that 

 seed. The dispersion of the fruit itself is sufficient. 

 The dehiscence of fruits, then, is determined by the 

 need for dispersing the contained seeds. It may be 

 laid down as a general rule that single-seeded fruits 

 are indehiscent, while fruits containing many seeds 

 open to allow of their discharge and distribution. 

 The dissemination of the fruit itself suffices where 

 the number of contained seeds is small. In some 

 plants two perfectly distinct modes of dispersion 

 occur - one for the distribution of the fruits, and the 

 other for the scattering of the individual seeds. 



Instead of opening to allow of the escape of its 

 seeds, a many-seeded fruit may break up into 

 indehiscent pieces, each piece containing a single 



