DEHISCENCE 115 



it must separate the wall of the cell into two parts, and this form is 

 called Lociilicidal dehiscence. By an intermediate form, the dehiscence 

 takes place at the point where the septum joins the outer wall (Fig. 317), 

 the IMarginicidal form. Various other modifications and combinations 

 of the two forms may be discovered, but do not call for a notice in this 

 work. 



Mechanism of Dehiscence.— Dehiscence is secured by a peculiar adap- 

 tation of the fil)ers to the other tissues and to the form of the fruit. 



Incomplete Dehiscence. — \^arious forms of imi)erfect or incomplete 

 dehiscence are those in which it commences at the apex and fails to 

 extend itself to the base, as in Cerastium (Fig. 318) and EvcalyjJtus 

 (Fig. 319), or in which it commences at the base and extends only 

 partially toward the apex, as in Jnssiaea (Fig. 321) and in Cinchona 

 (322). Important pharmaceutical decisions have rested upon the 

 question of basal or apical dehiscence. The true Cinchona barks have 

 all proceeded from species whose fruits dehisce as represented in Fig. 

 322, while those of the trees yielding the false barks dehisce as repre- 

 sented in Fig. 323. 



Syecial Terms for Dehiscence. — The manner in which true dehiscence 

 passes into false or transverse dehiscence, called Circumscissile, is well 

 displayed by Figs. 325, 32G, and 320, viewed in the order named, all 

 illustrations of closely related plants. A very curimis form of special 

 dehiscence is that of Jeffersonia (Fig. 327). 



Rupturing. — Dehiscence is not the only method by which fruits 

 open to discharge their seeds. Rupturing fruits are those which oj)en 

 by an irregular line. 



Dehiscence by Pores. — Some portion of a pericarp may decay quickly, 

 leaving an opening, or the same result may be secured by excessive 

 shrinkage in drying of the more delicate tissue of some part of the 

 Pericarp, as in Fig. 328. Openings of this kind are called Pores. Our 

 consideration of this subject will close with an illustration of the fruit of 

 the Bcrtholctia, or Brazil-nut (Fig. 324). The apex of this enormously 

 thickened and strongly hardened pericarp consists of a small circular 

 portion coiniected with the remainder by a circle of tissue which quickly 

 decays, making the former removable as a plug and thus leaving an 

 apical pore. 



