476 



HUTCHINSON'S POPULAR BOTANY 



days, and when the seeds are ripe, the teeth are curved back. The seeds 

 escape by this opening. 



Compare carefully the capsules depicted in figs. 586, 587, which are shown 

 in transverse section, and represent respectively the fruit of the Iris and 

 Meadow-saffron (Colchicum autumnale) : fig. 585 is a fruit of the Common 

 Thorn-apple (Datura stramonium). In fig. 588 the three forms are 

 shown diagrammatically. Now, in each of these examples it will be noticed 

 that the capsule dehisces in a different manner. In the Iris the capsule 

 splits through the back of its three seed-containing cavities (by its dorsal 

 suture, as we should say), and thus the cavities or loculi are broken open 



This is known as loculicidal dehiscence. Sep- 

 ticidal dehiscence is illustrated in the 

 Meadow-saffron. Here the carpel separates 

 into its component ovaries, each of the walls 

 of separation or dissepiments dividing into 

 two, and thus the loculi remain intact. In 

 the Thorn-apple there is no splitting of the 

 dissepiments, which remain attached to the 

 axis, but the carpellary wall which surrounds 

 them, and to which they are attached, breaks 

 away at the three points of attachment, and 

 so the seeds escape. This is septifragal de- 

 hiscence. 



From the circumstance that, in each of 

 the three examples here given, the pericarp 

 comes away in pieces or valves, the dehis- 

 cence is also said to be valvular. Allusion 

 has been made already to two very remark- 

 able instances of valvular dehiscence. The 

 sling-fruits both of Jmpatiens and of Oxalis 

 come under this category. In the former, 

 the mesocarp consists of large and highly 

 turgid cells, which keep the whole of the capsule in a state of great tension ; 

 so that when the fruit is touched the valves rly open, and eject the seeds 

 with considerable force ; in the latter, as we have seen, the bursting of the 

 elastic fieshy outer integuments of the seeds is the cause of their expulsion. 

 " On the heights of the Kahlenberg, at Vienna, at the edge of the wood,'' 

 says Kermer, grows an under-shrub which bears the name of Dorycnium 

 herbaceum. It is one of the Papilionacese, and develops spherical one-seeded 

 fruits, which ripen in October. I once collected from this plant several 

 twigs laden with fruit, for the purpose of a comparative investigation on 

 which I was engaged, and brought them home and laid them on my writing- 

 table. Next day as I sat reading near the table, one of the seeds of the 

 Dorycnium was suddenly jerked with great violence into my face. Shortly 



FIG. 585. THORN-APPLE (Datura). 



The carpellary wall alone splits and separates 

 from the dissepiments. Septifra.sal dehiscence. 



