ORGANS OP REPRODUCTION. 309 



the different wliorls of the flower, in a regular arrangement 

 alternate with each other, the component carpels of the fruit 

 should alternate \Yith the divisions or sepals of the calyx. If 

 the fniit therefore separates into as many portions as there are 

 parts or sepals to the calyx, and if these valves are then placed 

 alternate to them, they represent the component carpels, and 

 the dehiscence is consequently analogous to the septicidal form; 

 if, on the contrary, the A-alves are equal and opposite to the 

 divisions of the calyx, each valve is composed of the adjoining 

 halves of two carpels, and the dehiscence is analogous to 

 the loculicidal form. Sometimes the number of valves is double 

 that of the calycine segments, or sepals, in M'hich case, each 

 valve is formed of half a carpel, the dehiscence of the fruit 

 having taken place both by its dorsal and ventral sutures. 



In all the above forms of valvular dehiscence, the separa- 

 tion may either take place from above downwards, which is 

 by far the more usual form {figs. 654, 657, and G62); or occa- 

 sionally from below upwards, as in the Mahogany {Swietenia 

 Mahagoni), Chelidonium {fig. 667), Cruciferous Plants {fig. 

 666), &c. 



2. Transverse or Circumscissile Dehiscence. — In this 

 kind of dehiscence, the opening takes place by a transverse Une 

 through the fruit across the sutures, so that the upper parL is 

 separated from the lower like the lid of a 

 soap-box, as in Hyoscyamus {fig. 668), Fig. 668. 



AnagalHs {fig. 692), Purslane, &c. Some- 

 times the dehiscence only takes place half 

 round the fruit, as in Jejfersonia, in which 

 case the lid remains attached to the fruit on 

 one side, as by a hinge. The transverse de- 

 hiscence of fruits resembles certain forms of 

 calyx, as that of Eucalyptus and Eschschol- 

 tzia, Avhere the upper part separates from jF/g.668. FmitofHen- 

 the lower like a lid. The fruits or pericarps bane (Hyoscyamiui) 



, . , ^ ^ , , . ^ l with transverse de- 



which present transverse dehiscence may be idscence. This fruit 

 supposed to be formed, either of carpellarv '^, termed a pyxis, 



, ^ ^ . 1 • . , 1 • ■ 1 S wlucli IS a kind of 



leaves m which the laminre are articulated capsule, 

 to the petioles, as in the Orange {fig. 300), 

 and which become separated at the point of articulation, so 

 that the united petioles form the lower part of the fruit, and 

 the united lamina the upper; or it may result from the prolon- 

 gation and hollowing out of the thalamus, and the articulation 

 of the carpellary leaves to its circumference, so tliat in the 

 dehiscence the lower part of the fruit is formed by the concave 

 thalamus, and the upper p»art by the carpellary leaves; thus 

 resembling the separation of the calyx in Eschscholtzia from 

 the thalamus. 



x3 



