THE DEHISCENCE OF FRUITS 275 



essential in the latter stages, if the parts of the fruit are to 

 acquire the elasticity concerned in the forcible expulsion of the 

 seeds, but it is not necessary for seed-liberation. Seeing that 

 most fruits liberate their seeds without forcibly discharging 

 them in this manner, it may be doubted whether we should 

 specially regard such violent propulsion as purposive, 

 determined as it is largely by the degree of dryness of the air. 

 However this may be, it is evident from the above experi- 

 ments that other factors than those concerned with drying go 

 to determine the dehiscence of fruits. 



Though the phenomena are physical in origin, writes Pfeffer Prof. Pfeffer 

 {Physiology of Plants^ iii. 146-153), the development of the hiscence. 

 requisite physical conditions is a physiological problem. The 

 required instability, when mechanical agencies of external or of 

 internal origin may release the dehiscing organism, is produced 

 by growth, the requisite tissue-strains and the conditions for their 

 release being prepared by the vital activity of the organism. 

 The distinction which he draws between internal and external 

 agencies in the opening of dehiscent fruits coincides with one 

 of the principal differences between the modes of dehiscence 

 of legumes and many capsules, as indicated by my observations. 

 Whilst in the one case the opening of the capsule is often 

 brought about through the distension of its walls by the growth 

 of its seed-contents, in the other the dehiscence of the legume 



is usually caused by the strain generated in the drying process. The author's 

 T,^ 1111- 1 ..^°'' J observations. 



in the capsule the dehiscence, however arismg, corresponds 



with the maximum growth of the fruit. In the legume it 

 happens at a much later stage, namely, after its biological 

 connection with the parent has been more or less severed, 

 and when it has lost the greater part of its water by drying, 

 and in consequence its vitality. Regarding the difference The capsule 

 between the two processes from merely a physical standpoint, jj.jgs The 

 we can say that whilst the capsule dehisces and dries, the ^^53,is"el. 

 legume dries and dehisces. By removing a single letter we 

 can at the same time express the biological distinction by say- 

 ing that whilst the capsule dehisces and dies, the legume dies 



