STRUCTURE.] MONSTROUS DEHISCENCE TRANSVERSELY. 301 



by a dislocation of the cohering margins, but by another 

 very curious way of dehiscence. The ascidium formed an 

 elongated bag, tumid in the middle, tapering at its two 

 extremities, above and below ; now this bag was split across 

 with a horizontal rupture, just as in the ascidium the lid 

 is detached from the pitcher, or rather as in mosses the 

 calyptra falls off from the urn. The flower indeed carried 

 this cap with it, and could not rid itself of it, so that 

 the perianth remained curled up beneath and within. At 

 sight of this tulip, having at its base a conical foliaceous 

 hollow body, from the centre of which arose a long peduncle, 

 terminating in its turn in an another cone, which disclosed 

 the organs of fecundation, I could not help comparing it to a 

 large moss armed with its calyptra. In Nepenthes and 

 Sarracenia the ascidia also are at first shut up, and at Edin- 

 burgh, upon the beautiful plants of Nepenthes, cultivated 

 with so much skill by Mr. Mac Nab, I was able to learn how 

 their dehiscence takes' place. The part which the circular 

 struma acts, with its numerous small transverse ribs, then 

 becomes very easy to understand. Before the operculum is 

 detached, its thin margins are folded round this struma, 

 which holds them very strongly fixed, as a bladder is fastened 

 over the opening of a vessel by the infected margin. 



" When once the operculum is freed it cannot again fasten 

 itself above the struma. This dehiscence of the lid is there- 

 fore horizontal, or in a small degree oblique, like the direc- 

 tion of the struma itself, and it is nearly the same in all 

 ascidia. On that of the tulip formed by monstrosity, the 

 opening, although in this case it was an actual rupture 

 caused by internal violence, took place, notwithstanding, in 

 the same manner. This comparison deserves some atten- 

 tion, especially if further observations tend to confirm it." 

 (Annals of Natural History, III. 411.) 



To me this explanation is not entirely satisfactory, nor do 

 I believe that the pitchers of Sarracenia and Nepenthes 

 (fig. 58 A), have any analogy with the pitcher-like expansions 

 which frequently rise up from the surface of Cabbage leaves, 

 an example of which is figured in the Transactions of the 

 Horticultural Society, vol. V., t. 1. 



