ORIGIN OF ENDOGENS FROM EXOGENS. 511 



vascular bundles. They differ from Exogens in wanting liber, 

 wood-wedges, and medullary rays, and in the confused arrange- 

 ments o£ the vascular tissue ; and from Endogens in the vascular 

 zone surrounding a column of pith, in the arrangement of the 

 vascular fascicles and in their composition. Our conclusion was, 

 that the structure was quite reducible to a very low and deranged 

 type of exogenous stem, such as might be expected to occur in 

 an axis of which all the internodes are crowded into the smallest 

 possible compass, and in a plant the habit and general arrange- 

 ment of whose organs of support and nutrition differ so widely 

 from that of ordinary exogens/'* 



Analogous forms of degradation occur elsewhere. Thus, a 



— ^ v *~»« ^ v*v, 



feature of what may be called excessive degradation has been 

 noticed by botanists in several aquatic exogens and endogens, 

 which renders their structure more or less identical. Thus 

 M. Caspary has shown that Aldrovanda vesiculosa possesses the 

 same structure as submerged endogens, especially of the tribe 

 Hydrillex of Itydrocharidacece ; as, e.g., of Elodea canadensis t. 

 Similarly, M. van Tieghem points out t that TItricularia has 

 certain resemblances to endogens as follows : — fl L'axe du 

 faisceau est occupe par un unique vaisseau etroit forme par une 

 file de cellules superposees, a cloisons transverses fortement 

 obliques et imperforees ; ces cellules sont annelees, et leurs 

 anneaux assez espaces alternent g& et la avec quelques tours de 

 spire. Ce vaisseau appartient done a la classe des vaisseaux 

 imparfaits, sur lesquels M. Caspary a appele, en 1862, l'attention 

 speciaie des anatomistes, et qui, tres-repandus chez les Monoco- 

 tyledones, ou M. Mohl les decrivait dans les Palmiers des 1831, 

 sont tres-rares, au contraire, chez les Dicotyledones, ou leur pre- 

 sence exclusive dans tous les organs n'a e'te' signalee jusqua 

 present que dans Y Aldrovanda, le Monotropa, le Nelumbium et 

 les Nympheacees "§. M. van Tieghem adds in a note that he has 

 been assured that Gunnera^ a subaquatic plant, has also all the 

 vessels of the petiole of this description. Ceratophyllum may be 

 also compaied with Naias iu this respect. 



* Fl. Ind. i. p. 236. Later writers appear to confirm these views. See De 

 Bary's Coinp. Anat. p. 252. 



t Bull, de la Soc. bot. de Fr. 1858, p. 716; Bot. Zeit. 1859, 1862. 



t H Anatomie de l'Utriculaire commune," Ami. des Sei. Nat. 7> ser. torn. x. 

 1869, p. 54. 



Caspary, Monatsberichte der Berliner Akademie, Juillet 1862. 



LINN. JOUJ1N. BOTANY, VOL. XXIX. 2 P 



