THE DEHISCENCE OF FRUITS 277 



acting from within, such as the pressure of the seed-contents, 

 is highly probable. Full-grown fruits placed in water and 

 in wet moss commenced to dehisce in a few days, whilst 

 others left to dry on a table made no effort to open after 

 prolonged drying. 



With Iris Pseudacorus careful observation of the living Iris Pseuda- 

 plant convinced me that dehiscence as a rule occurs in moist, *^*"^^* 

 mellowing fruits, that is to say when the green capsule assumes 

 a yellowish tinge. Although, as already observed, the detached 

 fruits will dehisce in wet moss, this does not exclude altogether 

 the participation of the drying factor in the plant's natural 

 station by the water-side, where it is fully exposed to the sun. 

 If fruits dehisced in my experiments without drying, some of 

 them also opened after they had lost about 25 per cent, of 

 their weight exposed on my table. Nature does not follow 

 formularies in such matters ; and though internal causes mainly 

 determine the early dehiscence, we cannot entirely disregard 

 the influence of external conditions. The stages in the history 

 of the dehiscence of fruits normally maturing in September 

 would seem to be as follows : — 



(i) The full-grown green capsule, firm, full, and turgid ; 



(2) The capsule mellows, becoming yellowish and rather 



softer, which results in loosening the cohesion 

 between the valves ; 



(3) The dehiscence begins, determined by the pressure of 



the seed-contents, but aided by exposure to the sun 

 and by buffeting in the wind ; 



(4) The rapid drying of the fruit and the full exposure of 



the seeds. 



The results of one method of proving that capsular fruits A proof that 



dehisce in the moist condition are given in the subjoined dehfscehi 



table for Iris and for the Horse-chestnut. Here we find the moist 



, , r . . r • condition, 



that the fruit showing the first signs of dehiscence loses 



but slightly less in weight when dried in air than does the 



full-grown moist fruit with matured seeds that has not begun 



to open. 



