144 MOEPHOLOGY, OE COMPAEATITE ANATOMY. 



called coed, or where there are two, as in Umbellifers, mericarps (fig. 300). 

 More frequently the carpels not only separate septicidally but each one 

 bursts, through the dorsal suture, as in Geranium (tig. 276) ; or through 

 the ventral suture, as in Cokhicum. 



Dehiscence by teeth only differs from that by valves in the smaller 

 degree of separation. The fruits or seed-vessels of Caryophyllaceee 

 dehisce by teeth. Sometimes the teeth are equal in number to the carpels, 

 as when the dehiscence is through the ventral sutures only (Lychnis} ; 

 sometimes double the number of the carpels, when the splitting takes 

 place through both sutures (Diantlius) (fig. 273). 



Porous Dehiscence arises from the formation of orifices in 

 the walls of a dry capsule, allowing the seeds to escape. In the 

 Poppy (Pa/paver) a circle of pores is formed round the upper edge 

 of the fruit, just beneath the stigma ; in Antirrhinum and Linaria 

 there are two or three orifices near the summit of the capsule ; in 

 some Campanulas a pore is formed at the base of each cell. 



In all these cases the orifices are formed from thin spots in the walls, 

 which tear open, their edges curling back in more or less regular teeth : 

 the dehiscence of Antirrhinum is connected by that of Scrophularia, Diqi- 

 talis, &c. with the dehiscence into a crown of teeth as in Primula a'nd 

 Caryophyllaceae. 



Transverse or Circumscissile Dehiscence, observed in the mem- 

 branous capsules of Hyoscyamus (fig. 294), Anagallis (fig. 274), 

 Plantago, &c., and in the woody fruits of Leeythis, arises from a 

 transverse fissure running round the wall and splitting off the upper 

 part of the fruit like a lid. A dehiscence analogous to this occurs 

 in the lomenta of various LeguininosaB, which break across in several 

 places between the seeds. 



In these cases a kind of articulation is produced, by the tissue of the 

 pericarp remaining more delicate in the fine of dehiscence, so that it 

 becomes torn by the hygrometric contraction or expansion of the firmer 

 parts above and below, after the fruit has become mature. 



Period of Dehiscence. Dehiscence does not usually take place until 

 the seeds are ripe ; but in Mignonette (Reseda} the ovary opens before ; in 

 Leontice thalictroides the ovary bursts very early, and tlie seed ripens in a 

 naked condition. In Impatiens and some other plants dehiscence takes 

 place suddenly with considerable force, the valves separating and rapidly 

 curling up. In Elaterium the peduncle separates in a similar sudden way 

 from the ripe fruit, and the seeds are forcibly ejected. 



Fruit of Gymnosperms. In Gymnosperms there is of course no 

 proper dehiscence ; but in most cases the carpellary scales of the 

 female cones, which are separate to some extent during fertiliza- 

 tion, frequently close up together so as to form an apparently solid 

 body while the seeds are ripening, as in Pinus, Cupressus, Thuja, 

 &c. (fig. 309). The scales open again when the seeds are ripe, 



