RND0G1 NS. 



circumference. Winn there is no Limited circumference • d bj n I 



to an Endogen, then the curved spots, which arc sections of the « I\ 



are much more equally arranged, and arc less crowded at thecircumfen 

 Never is there any distinct column of pith, or medullary rays, or concentric 

 arrangement of the woody arcs : nor does the cortical integument of the 

 surface of endogenous Btems assume the character of bark, separal 

 the wood below it ; on the contrary, as the cortical integumenl 



much of the finely divided extremities of the « ly arcs, the) necessarily 



hold it fast to the w I. of which they arc themselves prolong . ami 



t!i rtical integumenl can only lie stripped off by tearing it away from the 



whole Burface of the wood, from which it does not separate without lea 

 myriads of little broken threads behind. 



Thi- i- the apparent and general structure of the most p< rfect a: 

 Endogens. It i- of course modified exceedingly according to the nature of 

 particular individuals, and may even he reduced to nullity, as i- the case in 

 Lemna, Tillandsia usneoides, Naiads, and similar plants. 



Schleiden, who treats this subject in a merely anatomical manner, thus 

 ribes the peculiarities of J'.mlogcns or Monocotyledons, and the manner 

 in which they differ from Exogens or Dicotyledo 



In all plants, he says, the woody bundles, whose development always 

 proceeds from the interior to the exterior, are either limited or unlimited 

 in their growth. Commonly everj woody bundle consists of three different 

 physiological parts ; firstly, of a tissue of extreme delicacy, capable of rapid 

 development, in which new cells are continually generated and deposited in 

 various ways, in two different directions, viz. next the circumference, in the 



sha] fa peculiar kind of lengthened cellular tissue with very thick wall-. 



the liber ; and next the centre, in the form of annular, spiral, reticulate, 

 and porous vessels : secondly, of woody cells, which are either uniform in 

 appearance, or different, and form the wood, properly SO called. Up to a 

 certain period the development of the vascular system in Monocotyledons 

 and Dicotyledons proceeds upon the same plan : hut in Monocotyledons (En- 

 dogens) the active, thin, solid, delicate cellular tissue, suddenly changes : the 

 partitions of it- cells become thicker ; their generating power < ; ami 



when all the surrounding cells are fully developed, they assume a peculiar 

 form, ceasing to convey gum, mucilage, and ether kind- of thick formative sap. 



From this cause all further development of vascular bundles i.- rendi 

 impossible, and therefore Schleiden call- the woody bundles of such plants 

 " limited." In Dicotyledons (Exogens), on the contrary, this tissui 

 during the whole lifetime of the plant, its vital power of formation : conti- 

 nues to develop new cell- ; and so increases the mass, c< lugiuent- 



ing both the exterior (liber), and the interior face- « I), for which 



reason Schleiden call- such woody bundles " unlimiti d. Tl on- 



tinues. happens according to the climate and nature of the plant : • 

 pretty continuously, as in Cactaceffi j or by abrupt periodical advance- and 

 cessations, as occurs in forest treesof Europe. In the latter, tl 

 an uninterrupted tissue, from the pith to the hark, during 

 life, and the hark is never organically -epaiate from the stem : wl at is con- 

 sidered their natural separation in the spring, is only a rent produced by 

 tearing the delicate tissue already spoken i f, which is present, even during 

 winter, and constitutes the foundation of new annr. though 



pressed, and filled with gum. starch, and other seer, tions. In thi 

 being expanded and swollen by the new current of sap, it i- deprh 

 contents hv their solution. 



