THE DEHISCENCE OF FRUITS 291 



are physical, the development of the requisite physical conditions is a 

 physiological problem. 



(3) Yet the different behaviour of capsules and legumes illustrates 

 the difference between external and internal causes in the dehiscence 

 of fruits. Whilst writh the capsule dehiscence takes place in the 

 ripening fruit as a relief to the tissue-strains developed by growth, in 

 the legume dehiscence usually presents itself as a relief to the tensions 

 developed by drying. Whilst the capsule dehisces and dries, the pod 

 dries and dehisces, the mechanism being concerned in the first case 

 with a living fruit and in the second case with a dead one. Amongst 

 the capsular fruits especially studied in this connection were those of 

 Msculus, Arenaria, Datura, Iris, Primula, Scilla, Stellaria, and Viola. 



(4) Dealing particularly with capsules, it is considered that the first 

 step in the relief of the strain produced by active growth is promoted 

 by the loosening of the cohesion of the valves affected in the mellow- 

 ing stage of the full-grown moist fruit. It is held that the normal 

 dehiscence of an actively growing fruit is physiologically impossiijle, 

 and that dehiscence could only occur after the biological connection with 

 the parent begins to be severed in the mellowing process. The nature 

 of the next stage depends on whether the seeds completely fill the fruit 

 cavity, as in Iris, or only partially fill it, as in Scilla and Arenaria. 

 In the first case the capsular walls, owing to the loosening of the 

 connection between the valves, are no longer able to respond to the 

 pressure of the seed-contents and gape widely during the subsequent 

 drying process. In the second case the drying completes the loosening 

 begun in the mellowing stage, but the valves remain more or less in 

 position. 



(5) Dehiscence may occur alike in the most watery of capsules, as 

 in Momordica, where the fruit-case holds 95 per cent, of water, and in 

 the hardest and most ligneous of capsular fruits, as with Mahogany 

 (Swietenia), where the water-percentage is 66, the dehiscence being 

 carried on in each case on the same regular plan as in Iris and in the 

 Horse-chestnut {Msculus). The dehiscence of the Mahogany fruit is 

 especially described, as well as that of Ravenala, another type of woody 

 capsule, in which last special questions are raised. 



(6) The contrast just drawn between the water-contents of the 

 pericarp or fruit-case of fleshy and woody capsules leads to the 

 discussion of a number of observations on different fruits, and stress is 

 laid on the point that even the driest-looking and most ligneous of 

 capsules hold more than 60 per cent, of water in the full-grown living 

 state. When, therefore, we speak of a capsule as a dry fruit, we really 

 have in our minds the dry dehisced fruit that has lost its vitality. 

 Dehisced capsules thus appear as dead or dying fruits ; and the 

 expression " dry fruit " has in their connection no biological significance 



